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Page 3
Contents
11 About This Book
12
What’s New in Xsan 1.4
12
Version Compatibility
14
Upgrading from an Earlier Version of Xsan
14
For More Information
15
Notation Conventions
17 Chapter 1: Overview of Xsan
17
What Is Xsan?
19
Xsan Storage Area Networks
21
Shared SAN Volumes
21
Controllers and Clients
22
SAN Connections
23
How Xsan Storage Is Organized
24
LUNs
25
Storage Pools
26
Volumes
28
Folders with Affinities
28
How Xsan Utilizes Available Storage
3
Page 4
28
Metadata and Journal Data
29
Striping at a Higher Level
30
Security
30
Expanding Storage
31
Xsan Capacities
33 Chapter 2: Setting Up a Storage Area Network
33
Hardware and Software Requirements
34
Supported Computers
34
Supported Storage Devices
35
Fibre Channel Fabric
36
Ethernet TCP/IP Network
37
Directory Services
38
Outgoing Mail Service
39
Planning Your SAN
41
Planning Considerations and Guidelines
50
Connecting Computers and Storage Devices
51
Preparing LUNs
51
Using the Xsan Admin Application
52
Installing Just the Xsan Admin Application
52
Connecting Through a Firewall
52
Xsan Admin Preferences
52
Getting Help
53
Using the Command Line
4
Contents
Page 5
53
SAN and Volume Setup Summary
54
Setting Up an Xsan Volume on a Storage Area Network
74
Renaming a SAN
75
Removing a SAN
75
Setting Up Additional SANs
77 Chapter 3: Managing SAN Storage
78
Adding Storage
79
Restoring the Previous Volume Configuration After Changes
79
About Rearranging Fibre Channel Connections
80
Adding LUNs to a Storage Pool
82
Adding a Storage Pool to a Volume
84
Adding a Volume to a SAN
86
Assigning a Storage Pool Affinity to a Folder
87
Assigning an Affinity to a Folder Within a Folder
89
Removing an Affinity
90
Changing Storage Pool Settings
91
Renaming a Storage Pool
92
Choosing the Types of Files Stored on a Storage Pool
92
Setting Storage Pool Stripe Breadth
94
Setting the Selection Method for Multiple Connections
95
Changing Volume Settings
96
Renaming a Volume
97
Setting the Block Allocation Size
Contents
5
Page 6
99
Setting the Volume Allocation Strategy
10 0
Enabling or Disabling Access Control Lists
101
Choosing the Windows ID Mapping Method
101
Checking Volume Fragmentation
10 2
Defragmenting a Volume
10 3
Checking the Integrity of a Volume
10 4
Repairing a Volume
10 5 Chapter 4: Managing Clients and Users
10 6
Adding a Client
10 7
Adding a Client to a StorNext SAN
10 8
Mounting a Volume on a Client
10 9
Controlling Client and User Access
10 9
Controlling Access to Folders on Volumes
110
Setting Up Access Control Lists
110
Unmounting a Volume on a Client
110
Restricting a Client to Read-Only Access
111
Removing a Client from a SAN
111
Removing Xsan Software from a Computer
112
Mapping Windows User and Group IDs
11 4
Setting User and Group Quotas
115
About Xsan Quotas
117
Checking User Quota Use
119
Helping Clients Check Their Own Quotas
6
Contents
Page 7
12 0
Creating Local Home Folders for Network Accounts
121 Chapter 5: Managing Metadata Controllers
12 2
Adding a Controller
12 3
Setting Controller Failover Priority
12 4
Switching to a Standby Controller
12 5
Finding Out Which Controller Is Hosting a Volume
12 7
Listing the Volumes Hosted by a Controller
12 8
Changing a Controller’s IP Address
12 9
Upgrading Controller Software
13 0
Monitoring Controller Status
131 Chapter 6: Monitoring SAN Status
13 2
Locking Xsan Admin Views for Secure Monitoring
13 3
Checking Overall SAN Status
13 4
Checking Overall Volume Status
13 5
Checking Free Space on a Volume
13 6
Checking Free Space on a Storage Pool
13 6
Checking Quota Use
13 6
Viewing a Controller’s CPU and Network Utilization
13 7
Viewing File System CPU and Memory Utilization
13 8
Setting Up Status Notifications
13 9
Checking the Status of File System Processes
13 9
Viewing Xsan Logs
Contents
7
Page 8
14 0
Checking Volume Clients
141
Checking for Fibre Channel Connection Failures
141
Checking the State of Xserve RAID Systems
14 3 Chapter 7: Solving SAN Problems
14 3
A Dialog on a Client Reports That a LUN Is Unreadable
14 3
You’re Unable to Connect to a Computer Using Xsan Admin
14 4
You’re Unable to Install the Xsan Software
14 4
Some Computers Aren’t Listed in Xsan Admin
14 4
You’re Unable to Mount a Volume on a Client
14 5
Xserve RAID LUNs Aren’t Accessible over Fibre Channel
14 5
You’re Unable to Restart a Volume After Adding LUNs or Storage Pools
14 6
Some LUNs Aren’t Listed in Xsan Admin
14 7
Some LUNs Are Listed Twice in Xsan Admin
14 7
Files and Folders Created by Mac OS 9 Computers Show the Wrong Creation Date
14 8
Problems Using Command-Line Tools
14 8
A LUN Doesn’t Have as Much Space as Expected
14 9
You’re Unable to Rename an Xsan Volume in the Finder
14 9
Fibre Channel Performance Is Poorer Than Expected
14 9
A Client User Sees Error Code –1425
14 9
File Copy Doesn’t Finish
15 0
A Client is Unable to Use a Volume After a Fibre Channel Interruption
15 0
SAN Performance Declines Periodically and Predictably
151
You’re Unable to Add a Storage Pool
8
Contents
Page 9
152
You’re Unable to Add LUNs to a Storage Pool
153
The Capacity of a Larger LUN is Listed as 2 Terabytes
155 Appendix A: Combining Xsan and StorNext Clients and Controllers
155
Terminology
15 6
Compatible Software Versions
15 6
Licensing
157
Adding Macintosh Clients to a StorNext SAN
159
Using Xsan Controllers with StorNext Clients
161 Appendix B: Using the Command Line
161
Using the Shell Commands
162
Sending Commands to Remote Computers
162
Viewing the Man Pages
163
Notation Conventions
164
The Commands
164
Viewing or Changing Volume and Storage Pool Settings (cvadmin)
168
Copying Files or Folders (cvcp)
171
Checking or Repairing a Volume (cvfsck)
17 2Labeling, Listing, and Unlabeling LUNs (cvlabel)
17 7Defragmenting a File, Folder, or Volume (snfsdefrag)
17 9Mounting an Xsan Volume
18 0Unmounting an Xsan Volume
181Viewing Logs
181 The Configuration Files
181Examples
183 Glossary
187 Index
10Contents
Page 11
About This Book
Use this guide to learn how to set up and manage Xsan
volumes on a storage area network.
This guide shows how to use Xsan to combine Xserve RAID arrays and slices into large,
easy-to-expand volumes of storage that clients use like local disks but are actually
shared over a high-speed Fibre Channel fabric.
Chapter 1 provides an overview of Xsan and how you can use it to organize RAID arrays
into shared volumes of storage.
Chapter 2 includes hardware and software requirements, SAN planning guidelines, and
basic steps for setting up an Xsan volume.
Chapter 3 contains instructions for expanding storage, creating folders with affinities,
changing volume and storage pool settings, and checking, defragmenting, and
repairing SAN volumes.
Chapter 4 shows how to add client computers to a SAN, mount volumes on clients,
control client and user access to SAN files, and control user space using quotas.
Chapter 5 contains information about managing volume metadata controllers.
Chapter 6 includes instructions for monitoring and automatically reporting the
condition of a SAN.
Preface
11
Page 12
Chapter 7 lists solutions to common problems you might encounter.
Appendix A contains information to help you combine Xsan controllers or clients with
ADIC StorNext controllers or clients on the same SAN.
Appendix B describes command-line utilities and configuration files you can use to
manage an Xsan SAN using Terminal.
What’s New in Xsan 1.4
Xsan 1.4 offers these new features and capabilities:
 You can use access control lists (ACLs) to manage user access to Xsan volumes.
 Xsan runs on Intel-based Macintosh computers.
Version Compatibility
The following table shows which versions of Xsan and StorNext controllers and clients
can be used on the same SAN.
Important: If you set up a LUN that is larger than 2 terabytes (TB), be aware that older
clients (those running Xsan on Mac OS X 10.3 Panther or Xsan 1.2 or earlier on
Mac OS X 10.4 Tiger) cannot read these large LUNs. A dialog appears on these older
clients that says the LUN is unreadable. Be sure to click Ignore to dismiss this dialog.
Do not click Format, or information on the corresponding Xsan volume will be lost.
If you use LUNs greater than 2 TB, you should upgrade all SAN clients to Xsan 1.3 or
later on Mac OS X or Mac OS X Server v10.4.
12Preface About This Book
Page 13
ControllerClientCompatible
Xsan 1.4 Xsan 1.4Yes
Xsan 1.3 (Mac OS X v10.4)Yes
Xsan 1.3 (Mac OS X v10.3)Yes, for LUNs < 2 TB
Xsan 1.2 or earlierNo
StorNext 2.8No
StorNext FX 1.3 or 1.4Yes
StorNext 2.6 or 2.7Yes
StorNext 2.5 or earlierNo
Xsan 1.3 (Mac OS X v10.4)Xsan 1.4No
Xsan 1.3 (Mac OS X v10.4)Yes
Xsan 1.3 (Mac OS X v10.3)Yes
StorNext FX 1.3 or 1.4Yes
StorNext 2.6 or 2.7Yes
StorNext 2.5 or earlierNo
StorNext 2.8Xsan 1.4 or 1.3Yes
StorNext 2.7Xsan 1.4 or 1.3Yes
StorNext 2.6 or earlierXsan 1.4 or 1.3No
Preface About This Book13
Page 14
Upgrading from an Earlier Version of Xsan
For more information about migrating your SAN storage to Xsan 1.4 from an earlier
version of Xsan, including tips for upgrading with the least impact on existing storage,
see the Xsan Migration Guide at www.apple.com/server/documentation/.
For More Information
For more information about Xsan, consult these resources:
Read Me documents—important updates and special information. Look for them on the
Xsan installation disc.
Xsan website (www.apple.com/xsan/)—gateway to extensive product and technology
information.
Xsan Support website (www.apple.com/support/xsan/)—access to articles about Xsan
from Apple’s support organization.
Apple customer training (train.apple.com/)—instructor-led and self-paced courses for
honing your Xsan administration skills.
Apple discussion groups (discussions.info.apple.com/)—a way to share questions,
knowledge, and advice with other Xsan administrators.
Apple mailing list directory (www.lists.apple.com/)—subscribe to mailing lists so you can
communicate with other Xsan administrators using email.
14Preface About This Book
Page 15
Notation Conventions
The following conventions are used in this book wherever shell commands or other
command-line items are described.
NotationIndicates
fixed-width fontA command or other terminal text
$A shell prompt
[text_in_brackets] An optional parameter
(one|other)Alternative parameters (type one or the other)
underlinedA parameter you must replace with a value
[...]A parameter that may be repeated
<angle_brackets>A displayed value that depends on your SAN configuration
Preface About This Book15
Page 16
Page 17
1 Overview of Xsan
This chapter gives you an overview of Xsan and storage area
networks.
Read this chapter for an overview of Xsan and how you can use it to set up a storage
area network (SAN) to provide fast, shared storage.
What Is Xsan?
Xsan is a storage area network file system and a management application (Xsan
Admin) that you can use to provide users or applications on client computers with
shared high-speed access to expandable storage.
1
17
Page 18
Xsan lets you
combine RAID arrays
into volumes clients
use like local disks.
Storage
pools
RAID
arrays (LUNs)
18Chapter 1 Overview of Xsan
Mac OS X
San Volume
File data moves
over Fibre Channel
Page 19
Xsan Storage Area Networks
A storage area network is a way of connecting computers to storage devices that gives
users very fast access to files and gives administrators the ability to expand storage
capacity as needed without interrupting users.
An Xsan SAN consists of:
 Volumes of shared storage, stored on Xserve RAID systems, available to clients as
mounted volumes that they can use like local disks
 At least one computer acting as a metadata controller that coordinates access to the
shared volumes
 Client computers that access storage in accordance with established permissions and
quotas
 Underlying Fibre Channel and Ethernet networks
The following illustration shows the physical components of a typical Xsan SAN.
Chapter 1 Overview of Xsan19
Page 20
Metadata
controller
Clients
Ethernet - TCP/IP (Public)
Ethernet - TCP/IP (Private)
20Chapter 1 Overview of Xsan
Standby
controller
Fibre
Channel switch
Xserve RAID
storage
Intranet/
Internet
Page 21
Shared SAN Volumes
Users and applications see shared SAN storage as local volumes. Xsan volumes are
logical disks made up of groups of RAID arrays. The elements you combine to create an
Xsan volume are described under “How Xsan Storage Is Organized” on page 23.
Controllers and Clients
When you add a computer to an Xsan SAN, you specify whether it will play the role of
client, controller, or both.
Controllers
When you set up an Xsan SAN, you assign at least one computer to act as the
controller. The controller manages the SAN volume metadata, maintains a file system
journal, and controls concurrent access to files. Metadata includes such information as
where files are actually stored and what portions of available storage are allocated to
new files.
For high availability, you should add more than one controller to a SAN, as shown in
the illustration on page 20. If the primary controller fails, the standby controller takes
over. Though not recommended for best performance, controllers can also act as
clients, so you can use a standby controller as a working client while the primary
controller is operational.
Clients
The computers that users or applications use to access SAN volumes are called clients.
Clients communicate with controllers over the Ethernet network but use Fibre Channel
to send and retrieve file data to and from the RAID systems that provide storage for the
volumes.
Chapter 1 Overview of Xsan21
Page 22
SAN Connections
Xsan uses independent networks to connect storage devices, metadata controllers, and
client computers: a Fibre Channel network and one or two Ethernet networks.
User Data Over Fibre Channel
User data is transferred over high-speed Fibre Channel connections. Controllers also
use a Fibre Channel connection to move metadata to and from the volume.
Metadata Over Ethernet
To eliminate unnecessary traffic on the Fibre Channel connections, controllers and
clients use an Ethernet network to exchange file system metadata. (When a controller
reads or writes metadata on a volume, it uses Fibre Channel.) The Xsan Admin
application also uses the Ethernet connection to let you manage the SAN.
To prevent Internet or intranet traffic from interfering with metadata communications,
you should set up separate Ethernet networks as shown in the illustration on page 20.
Fibre Channel Multipathing
Xsan can take advantage of multiple Fibre Channel connections between clients and
storage. Xsan can alternate between connections for each read and write, or assign
each LUN in a volume to one of the connections when the volume is mounted.
22Chapter 1 Overview of Xsan
Page 23
How Xsan Storage Is Organized
Users use an Xsan volume the same way they use a local disk. What they don’t see is
that the SAN volume actually consists of numerous physical disks combined on several
levels using RAID techniques.
The following illustration shows an example of how disk space provided by the
individual drive modules in several Xserve RAID systems is combined into a volume
that users see as a large local disk.
Faster
AffinityAffinity
Storage pool
(Striping)
LUNLUN
RAID 0
RAID 0
array
array
Chapter 1 Overview of Xsan23
LUNLUN
RAID 0
array
Safer
RAID 0
array
Shared
SAN volume
LUNLUN
RAID 5
array
Storage pool
(Striping)
RAID 5
array
LUNLUN
RAID 5
RAID 5
array
array
Page 24
The following paragraphs describe these storage elements and how you organize them
to create shared Xsan volumes.
LUNs
The smallest storage element you work with in Xsan is a logical storage device called a
LUN (a SCSI logical unit number). In most storage area networks a LUN represents a
group of drives such as a RAID array or a JBOD (just a bunch of disks) device. In Xsan,
LUNs are Xserve RAID arrays or slices.
You create a LUN when you use the RAID Admin application to create an Xserve RAID
array. The controller hardware and software in the Xserve RAID system combine
individual drive modules into an array based on the RAID scheme you choose. Each
array appears on the network as a separate LUN. If you slice an array, each slice appears
as a LUN.
One of your first tasks when you set up a SAN volume is to prepare LUNs. If the two
RAID 5 arrays on a new Xserve RAID are not right for your application, you can use
RAID Admin to create arrays based on other RAID schemes. For help choosing schemes
for your LUNs, see “Choosing RAID Schemes for LUNs” on page 44.
The illustration on page 23 shows four Xserve RAID systems that each host two arrays.
Half of the arrays use a RAID 0 scheme (striping only) for speed while the others use
RAID 5 (distributed parity) to ensure against data loss. Xsan sees the arrays as LUNs that
can be combined to create a volume.
After your Xserve RAID LUNs are set up, you label and initialize them for use with the
Xsan file system using Xsan Admin.
24Chapter 1 Overview of Xsan
Page 25
Storage Pools
LUNs are combined to form storage pools. A storage pool in a small volume might
consist of a single RAID array, but storage pools in many volumes consist of multiple
arrays.
Xsan distributes file data in parallel across the LUNs in a storage pool using a RAID 0
(striping) scheme. So, you can improve a client’s access speed by distributing available
storage over several LUNs in a storage pool.
You can set up storage pools that have different performance or recoverability
characteristics and assign folders to them using affinities. Users can then select where
to store files based on their need for speed or safety. See “Folders with Affinities” on
page 28.
The illustration on page 23 shows eight LUNs combined into two storage pools, one
pool consisting of RAID 0 (fast, but not recoverable) arrays and the other made up of
RAID 5 (not as fast, but recoverable) arrays. Xsan stripes data across the four LUNs in
each storage pool.
You use Xsan Admin to add available LUNs to specific storage pools.
Chapter 1 Overview of Xsan25
Page 26
Volumes
Storage pools are combined to create the volumes that users see. From the user’s
perspective, the SAN volume looks and behaves just like a large local disk, except that:
 The size of the volume can grow as you add underlying arrays or storage pools
 Other users on the SAN can access files on the volume at the same time
In the illustration on page 23, two storage pools are combined to create a single shared
volume.
You create volumes and mount them on client computers using the Xsan Admin
application.
26Chapter 1 Overview of Xsan
Page 27
The following screen image shows how LUNs, storage pools, and volumes appear as
you organize them in Xsan Admin. This example shows a SAN named “Editing SAN”
with a single shared volume named “SanVol.” Storage for the volume is provided by
two storage pools, “Meta” and “Data,” the first based on a single LUN and the second on
two. Each of the LUNs is a 3-disk RAID 5 array on an Xserve RAID using 115 GB drive
modules.
SAN
Volume
LUN
Storage pool
Chapter 1 Overview of Xsan27
Page 28
Folders with Affinities
To control which storage pool is used to store specific files (for example, to provide
different levels of service for different users or applications), you can associate a folder
on an Xsan volume with one of the storage pools that make up the volume.
If, for example, you set up storage pools with different balances of performance and
data redundancy, users can choose between faster and safer storage by putting files in
the appropriate folder.
In the illustration on page 23, a predefined folder has an affinity for the faster storage
pool that is based on RAID 0 arrays. Any file that a user copies into this folder is
automatically stored on the faster arrays. A second folder is associated with the more
secure RAID 5 storage.
How Xsan Utilizes Available Storage
Xsan stores both user files and file system data on SAN volumes, and stripes data
across the LUNs in a volume for better performance.
Metadata and Journal Data
Xsan records information about the files in an Xsan volume using metadata files and
file system journals. File system metadata includes information such as which specific
parts of which disks are used to store a particular file and whether the file is being
accessed. The journal data includes a record of file system transactions that can help
ensure the integrity of files in the event of a failure.
28Chapter 1 Overview of Xsan
Page 29
These files are managed by the Xsan metadata controller, but are stored on SAN
volumes, not on the controller itself. By default, metadata and journal data are stored
on the first storage pool you add to a volume. You can use Xsan Admin to choose
where these files are stored when you add storage pools to a new volume.
Striping at a Higher Level
When you write a file to a RAID array using RAID 0 (striping), the file is broken into
segments that are spread across the individual disk drives in the array. This improves
performance by writing pieces of the file in parallel (instead of one piece at a time) to
the individual disks in the array. Xsan applies this same technique at a second, higher
level in the storage hierarchy. Within each storage pool in a volume, Xsan stripes file
data across the individual LUNs that make up the storage pool. Once again,
performance is improved because data is written in parallel.
You can tune SAN performance by adjusting the amount of data written to each LUN in
a storage pool (the “stripe breadth”) to suit a critical application.
Chapter 1 Overview of Xsan29
Page 30
Security
As the SAN administrator, you can control access to shared volumes in several ways.
First, users cannot browse or mount SAN volumes. Only a SAN administrator can
specify which volumes are mounted on which client computers. One way you can
control access to data is to mount a volume only on appropriate client computers.
To prevent users from modifying data on a volume, you can mount the volume with
read-only access.
You can control user access to folders on a volume by setting up access control lists
(ACLs) in Workgroup Manager or by specifying owner, group, and general access
permissions in the Finder.
You can also set up zones in the underlying Fibre Channel network to segregate users
and volumes.
Expanding Storage
There are two ways you can add free space to an Xsan volume:
 Add Xserve RAID systems (new LUNs) to existing storage pools
 Add entire new storage pools to volumes
Both methods require you to unmount and remount the volume on clients.
You can also add new volumes to a SAN at any time.
For information about expanding Xsan storage, see “Adding Storage” on page 78.
30Chapter 1 Overview of Xsan
Page 31
Xsan Capacities
The following table lists limits and capacities for Xsan volumes.
ParameterMaximum
Number of computers on a SAN (controllers and clients)64
Number of storage pools in a volume512
Number of LUNs in a storage pool32
Number of LUNs in a volume512
Number of files in a volume4,294,967,296
LUN sizeLimited only by the size of the
Volume sizeLimited only by the number
File sizeApproximately 2
Volume name length70 characters
File or folder name length251 characters
SAN name length255 characters
Storage pool name length255 characters
LUN name (label or disk name)242 characters
Chapter 1 Overview of Xsan31
RAID array
and size of LUNs
63
bytes
Page 32
Page 33
2 Setting Up a Storage Area Network
This chapter lists requirements, suggests planning tips, and
gives instructions for setting up an Xsan SAN.
This chapter contains:
 Xsan hardware and software requirements (page 33)
 Planning guidelines (page 39)
 SAN setup instructions (page 53)
Hardware and Software Requirements
Your SAN environment needs to satisfy requirements in these areas:
 Supported computers
 Supported storage devices
 Fibre Channel fabric, adapters, and switches
 Ethernet network
 Directory services (optional)
 Outgoing mail service (optional)
2
33
Page 34
Supported Computers
You can use Xsan 1.4 on computers that meet these minimum requirements:
Systems
 Macintosh computers with an Intel or PowerPC G5 processor
Memory
 Clients should have a minimum of 256 MB of RAM.
 Controllers should have a minimum of 512 MB of RAM. For optimum performance,
add an additional 512 MB of RAM for each SAN volume hosted by the controller.
Supported Operating Systems
You can install Xsan 1.4 only on computers running
 Mac OS X or Mac OS X Server v10.4.7 or later
To join an Xsan 1.4 SAN, Windows, AIX, IRIX, Linux, and Solaris clients must be running
ADIC’s StorNext File System version 2.6 or 2.7. For complete compatibility information,
see “Version Compatibility” on page 12.
Supported Storage Devices
Although you can use any standard LUN storage device, this guide assumes you are
using Xserve RAID systems for your storage devices.
Important: Be sure to install the latest firmware update on your Xserve RAID systems
before you use them with Xsan.
For the best performance, use Xserve RAID systems that have:
 A full set of 14 Apple Drive Modules
 512 MB of cache in each controller (1 GB total)
34Chapter 2 Setting Up a Storage Area Network
Page 35
Fibre Channel Fabric
Unlike file system metadata, which controllers and clients exchange over Ethernet,
actual file content in an Xsan SAN is transferred over Fibre Channel connections (as is
metadata that controllers access on a volume). To set up the connections, you need:
 Apple Fibre Channel PCI, PCI-X, or PCI-E cards for each client and controller computer
 One or more supported Fibre Channel switches
 Fibre Channel cables connecting computers and storage devices to the switches to
form a Fibre Channel fabric
Fibre Channel PCI Cards
Install Apple Fibre Channel PCI, PCI-X, or PCI-E cards in all Macintosh computers that
will connect to the SAN.
Fibre Channel Switches
The following Fibre Channel switches have been tested with Xsan, Xserve RAID
systems, and the Apple Fibre Channel PCI, PCI-X, and PCI-E cards:
 Brocade Silkworm 3200, 3800, 3900, and 12000 series
 QLogic SANbox 2–8, SANbox 2–16, SANbox 2–64, SANbox 1400, and SANbox 5200
 Emulex SAN Switch 355, 375, and 9200
 Cisco MDS 9000 family
For the latest additions to this list of qualified switches, see the Xsan webpages at
www.apple.com/xsan/.
Chapter 2 Setting Up a Storage Area Network35
Page 36
Fabric Configuration
You must connect the computers, storage devices, and switches in your Fibre Channel
network to form a Fibre Channel “fabric.” In a fabric, Fibre Channel cables connect node
ports (F or N_Port). See the documentation that came with your Fibre Channel
switches for more information.
Note: If you are using a Vixel 355 switch, you must connect Xserve RAID systems to an
FL (arbitrated loop) port on the switch.
You cannot use Fibre Channel Arbitrated Loop (FL ports) with an Xsan SAN, with the
exception noted above for Vixel 355 switches.
Ethernet TCP/IP Network
Computers on the SAN must also be connected to an Ethernet network. Xsan uses this
network instead of the Fibre Channel network to transfer file system metadata,
reserving the Fibre Channel connections for actual file contents.
If the computers on your SAN need to communicate with directory servers, a corporate
or campus intranet, or the Internet, you should connect each SAN client and controller
to two separate Ethernet networks: one private subnet for the SAN and a separate
connection for directory, intranet, or Internet traffic. This is important if you plan to use
the SAN for high-performance applications such as video editing.
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IP Addresses and Domain Names
Assign fixed, non-routed IP addresses to all clients, controllers, and storage devices
connected to the SAN Ethernet network. Don’t use DHCP to assign addresses to SAN
devices. You can use the following ranges of IP addresses on your private (non-routed)
subnet:
If you plan to use user and group privileges to control access to files and folders on the
SAN, you can simplify management by setting up or joining a user and group directory.
Although not required, a central directory lets you manage users and groups on one
computer instead of having to visit all SAN clients and controllers.
If you already have a directory service, you can use the Directory Access application on
each controller and client to access the directory for user and group information.
If you don’t use a central directory service, you need to set up users and groups on
each SAN computer.
Important: If you create users and groups on each SAN computer, be sure that 1) each
user or group has a numeric user ID (UID) or group ID (GID) that is unique throughout
the SAN and 2) each user or group defined on more than one computer has the same
UID or GID on each computer.
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If you don’t have access to a directory service, you can use the directory services in
Mac OS X Server to set up an LDAP directory of SAN users and groups.
Note: If you do create your user accounts in a centralized directory, be aware that
some applications running on SAN client computers, such as Final Cut Pro, for example,
work better when users have local home folders. For help setting up local home folders
for users with network accounts, see “Creating Local Home Folders for Network
Accounts” on page 120.
Outgoing Mail Service
Xsan can send SAN status notifications via email on your local subnet or corporate
network without using a separate mail server. However, to send notifications outside
your local network, you need an SMTP server to act as a mail gateway. If you don’t have
access to an outgoing mail server, you can use the mail service in Mac OS X Server to
set one up.
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Planning Your SAN
It’s easy to add storage to an existing Xsan SAN, but reorganizing a SAN after you set it
up is not so simple. So, it’s important to plan the layout and organization of your SAN
and its storage before you set it up.
An Xsan SAN is composed of:
 Storage devices (usually Xserve RAID systems)
 LUNs (logical unit numbers, usually RAID arrays)
 Storage pools (groups of LUNs)
 Volumes (groups of storage pools visible to users)
 Clients (computers that use volumes)
 Controllers (computers that manage volume metadata)
 Underlying Fibre Channel and Ethernet networks
Before you use Xsan Admin to set up a SAN, decide how you want to organize these
components. Take the time to create a drawing or a table that organizes available
hardware into RAID arrays, storage pools, volumes, client computers, and controllers in
a way that meets both your users’ needs and your needs as the SAN administrator.
Then, consider the following questions.
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Preliminary Planning Questions
 How much storage do you need?
 How do you want to present available storage to users?
 What storage organization makes the most sense for user workflow?
 What levels of performance do your users require?
 How important is constant availability?
 What are your requirements for security?
Your answers to the above questions will help you decide the following:
 What RAID schemes should you use for your RAID arrays?
 How many SAN volumes do you need?
 How should individual volumes be organized?
 Which LUNs go in each storage pool?
 Which storage pools make up each volume?
 Which clients, users, and groups should have access to each volume?
 Which computers will act as controllers?
 Do you need standby controllers?
 Do you want to use controllers as clients also?
 Where do you want to store file system metadata and journal data?
 What allocation strategy should you use?
Review the considerations and guidelines on the following pages for help translating
your answers into a suitable SAN design.
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Planning Considerations and Guidelines
The following paragraphs might help you make some of your SAN design decisions.
How Much Storage?
Because it’s easy to add storage to an Xsan SAN, you only need to decide on an
adequate starting point. You can then add storage for user data as needed.
You can’t expand a storage pool that is used to store volume metadata and journal
data. For information about estimating your metadata and journal data storage
requirements, see “Estimating Metadata and Journal Data Storage Needs” on page 50.
Note that the number of Xserve RAID systems you use affects not only available space
but also SAN performance. See “Performance Considerations,” below.
How Should Users See Available Storage?
If you want the users working on a particular project to see a volume dedicated to their
work, create a separate volume for each project. If it’s acceptable for a user to see a
folder for his or her work on a volume with other peoples’ folders, you can create a
single volume and organize it into project folders.
Workflow Considerations
How much file sharing is required by your users’ workflow? If, for example, different
users or groups work on the same files, either simultaneously or in sequence, it makes
sense to store those files on a single volume to avoid having to maintain or hand off
copies. Xsan uses file locking to manage shared access to a single copy of the files.
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Performance Considerations
If your SAN supports an application (such as high resolution video capture and
playback) that requires the fastest possible sustained data transfers, design your SAN
with these performance considerations in mind:
 Set up the LUNs (RAID arrays) using a RAID scheme that offers high performance. See
“Choosing RAID Schemes for LUNs” on page 44.
 Group your fastest LUNs in storage pools reserved for the application. Reserve slower
devices for a volume dedicated to less demanding or supporting applications.
 To increase parallelism, spread LUNs across different Xserve RAID controllers. For
example, instead of creating a single 4-disk LUN on one side of an Xserve RAID, create
two 2-disk LUNs, one on each side, and add these LUNs to a storage pool. Xsan then
stripes data across the two LUNs and benefits from simultaneous transfers through
two controllers.
 To increase parallelism in a relatively small storage pool (the size of one or a few drive
modules), create a slice of similar size across all the drives on a controller instead of
creating the storage pool from just one or two drive modules.
 Spread file transfers across as many drives and RAID controllers as possible.
Try creating slices across the drives in RAID systems, and then combine these slices
into a storage pool.
 To increase throughput, connect both ports on client Fibre Channel cards to the
fabric and set the multipathing method for the storage pool to Rotate.
 Store file system metadata and journal data on a separate storage pool from user
data, and make sure the metadata LUNs are not on the same RAID controller as any
user data LUNs.
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 Use a router to isolate the Ethernet network used by the SAN from a company
intranet or the Internet, or better, use a second Ethernet network (including a second
Ethernet card in each SAN computer) for the SAN.
 If your SAN uses directory services, mail services, or other services on a separate
server, use a second, separate Ethernet network to connect SAN computers to that
server.
 As a rule of thumb, consider that a single Xserve RAID controller, after file system
overhead, can transfer roughly 80 MB of user data per second (160 MB per Xserve
RAID system). If your SAN must support an application running on multiple clients
that requires specific throughput on each client, you can use this number to estimate
the number of Xserve RAID systems necessary to support the aggregate transfer rate.
Availability Considerations
If high availability is important for your data, set up at least one standby controller in
addition to your primary controller. Also, consider setting up dual Fibre Channel
connections between each client, controller, and storage device using redundant Fibre
Channel switches.
Important: Losing a metadata controller without a standby can result in the loss of all
data on a volume. A standby controller is recommended.
Also, if you have a standby controller, you can upgrade the Xsan software without
interrupting the SAN. For more information, see “Upgrading Controller Software” on
page 129.
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Security Considerations
If your SAN will support projects that need to be completely secure and isolated from
each other, you can create separate volumes for each project to eliminate any
possibility of the wrong client or user accessing files stored on a volume.
As the SAN administrator, you control which client computers can use a volume. Clients
can’t browse for or mount SAN volumes on their own. You use Xsan Admin to specify
which clients a volume is mounted on.
You can also set up access control lists (ACLs) in Workgroup Manager or assign user
and group permissions to folders using standard file access permissions in the Finder.
Choosing RAID Schemes for LUNs
Much of the reliability and recoverability of data on a SAN is not provided by Xsan itself
but by the RAID arrays you combine to create your storage pools and volumes. Before
you set up a SAN, you use the RAID Admin application to prepare LUNs based on
specific RAID schemes.
Important: If a LUN belonging to an Xsan volume fails and can’t be recovered, all data
on the volume is lost. It is strongly recommended that you use only redundant LUNs
(LUNs based on RAID schemes other than RAID 0) to create your Xsan volumes.
LUNs configured as RAID 0 arrays (striping only) or LUNs based on single drives are
difficult or impossible to recover if they fail. Unprotected LUNs such as these should
only be used for volumes that contain scratch files or other data that you can afford
to lose.
Xserve RAID systems ship already configured as recoverable RAID 5 arrays.
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Xserve RAID supports all popular RAID levels. Each RAID scheme offers a different
balance of performance, data protection, and storage efficiency, as summarized in the
following table.
RAID level
RAID 0HighestVery HighHighestNo
RAID 1LowHighMediumYes
RAID 3High to very high MediumMediumYes
RAID 5High to very high HighHighYes
RAID 0+1LowHighHighYes
Storage
efficiency
Read
performance
Write
performance
Data
redundancy
RAID 10, 30, and 50 schemes assume the use of AppleRAID software striping and aren’t
appropriate for use with Xsan, which performs its own striping. For more help choosing
RAID schemes for your arrays, see the Xserve RAID User’s Guide or the Xserve RAID Technology Overview (at www.apple.com/server/documentation/).
Deciding on the Number of Volumes
A volume is the largest unit of shared storage on the SAN. If your users need shared
access to files, you should store those files on the same volume. This makes it
unnecessary for them to pass copies of the files among themselves.
On the other hand, if security is critical, one way to control client access is to create
separate volumes and mount only the authorized volume on each client.
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For a more typical balance of security and shared access, a flexible compromise is to
create a single volume and use folder access privileges or access control lists in
Mac OS X Server’s Workgroup Manager to control access.
Deciding How to Organize a Volume
You can help users organize data on a volume or restrict users to specific areas of the
volume by creating predefined folders. You can control access to these folders by
assigning access permissions using Xsan Admin.
You can assign folders to specific storage pools using affinities. You can, for example,
create a folder for data that requires fast access and assign that folder to your fastest
storage pool.
Assigning LUNs to Storage Pools
You should set up a storage pool using LUNs that have similar capacity and
performance characteristics.
To provide high performance, Xsan uses the RAID 0 scheme to stripe data across the
LUNs in a storage pool. This requires that the LUNs in the pool be the same size. If you
set up a storage pool using LUNs of different sizes, Xsan uses available space on each
LUN equal to the capacity of the smallest LUN. If the LUNs vary in size, this can result in
wasted capacity. For example, if you assign 240 GB and 360 GB RAID arrays to a storage
pool, 120 GB of the larger array will not be used. By combining LUNs with similar
capacities, you avoid wasting available storage.
If you want to set up a storage pool for use by a high performance application, assign
similarly high speed LUNs. Assign slower LUNs to a storage pool where you keep data
that doesn’t have critical performance requirements.
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Creating storage pools from LUNs that are hosted on different drive modules and
different RAID controllers increases performance by increasing the parallelism of data
transfers. For example, a storage pool consisting of two LUNs, each a single drive
module on the left side of an Xserve RAID, will not be as fast as a similarly sized storage
pool made up of two LUNs that are single slices across all seven drives, one slice on
each controller. In the first case, all transfers go through a single RAID controller to just
two drives; in the second case the same transfer is spread across two RAID controllers
and fourteen drives.
Assigning Storage Pools to Volumes
After you decide how to combine available LUNs into storage pools, assign the storage
pools to the volumes you want to create.
For best performance, create a separate storage pool just for file system metadata and
journal data.
Deciding Which Clients to Mount a Volume On
If you create multiple volumes, decide which volumes should be mounted on which
clients.
Choosing Controllers
You must choose at least one computer to be the SAN controller, the computer that is
responsible for managing file system metadata.
Note: File system metadata and journal data are stored on the SAN volume, not on the
controller itself. For more information, see “Choosing Where to Store Metadata and
Journal Data” on page 49.
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If you have a small number of clients or if performance is not critical you can use a
single computer as both controller and client. You can even set up a SAN consisting of
a single storage device and a single computer that acts as both controller and client (to
provide network attached storage, for example).
If high availability is important, you should use at least two controllers, one as the
primary controller and one as a standby. You can specify additional controllers as
needed, and set their failover priorities to determine the order in which they are tried if
the primary controller stops responding.
If performance is critical, don’t run other server services on the metadata controller and
don’t use the controller itself to reshare a SAN volume using AFP or NFS.
Choosing Standby Controllers
To be sure that SAN volumes are always available, set up at least one standby controller
that can take over if your primary metadata controller fails. A standby controller also
makes it possible for you to upgrade software on the controllers without interrupting
user access to SAN volumes.
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Combining Clients and Controllers
The same computer can function as both a metadata controller and a client. It’s
possible, for example, to set up a SAN consisting of a single Xserve RAID and one
computer that acts as both controller and client. Any computer you specify as a
controller can also act as a client.
If, for example, you don’t have a computer to dedicate as a standby controller, you can
assign a computer that is normally used as a client to take over controller duties if the
primary controller fails.
To keep clients and controllers separate, you can set up client-only computers for your
users.
Choosing Where to Store Metadata and Journal Data
The metadata and journal data that describe a volume are not stored on the volume’s
metadata controller but on the volume itself. By default, they are stored on the first
storage pool in the volume. If the volume consists of more than one storage pool,
you can choose which storage pool is used to store metadata and journal data.
In most cases, storing metadata and journal data on the same storage pool as user
data results in adequate performance. However, for the best possible performance,
store metadata and journal data on a separate storage pool within the volume and
make sure that the LUNs used are connected to a different RAID controller than the
LUNs that make up user data storage pools.
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Estimating Metadata and Journal Data Storage Needs
To estimate the amount of space required for Xsan volume metadata, assume that
10 million files on a volume require approximately 10 gigabytes of metadata on the
volume’s metadata storage pool.
Choosing an Allocation Strategy
The allocation strategy you choose for a volume determines the order in which its
storage pools are filled with data. You can choose round robin, fill, or balance.
If you choose round robin, Xsan writes new data in turn to each storage pool in
the volume.
If you choose fill, Xsan writes all new data to the first storage pool in the volume until
that storage pool is full, and then moves to the next storage pool. This is a good choice
if you want to keep a particular storage pool unused as long as possible.
If you choose balance, Xsan writes new data to the storage pool with the most
free space.
Connecting Computers and Storage Devices
Before you set up your Xsan SAN, connect client computers, controller computers, and
storage devices to the SAN’s Fibre Channel and Ethernet networks. Make sure your
networks meet the requirements summarized under “Fibre Channel Fabric” on page 35
and “Ethernet TCP/IP Network” on page 36.
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Preparing LUNs
Xserve RAID systems usually come preconfigured with two RAID 5 arrays, one on
each side (on each controller). So, out of the box, each Xserve RAID provides two LUNs.
If this suits your needs, no other preparation is needed.
If you want to set up some other combination of RAID arrays or slices, you need to do
so using the RAID Admin application before you can add the resulting LUNs to your
SAN’s storage pools. For help using RAID Admin, see Using RAID Admin 1.2 and Disk Utility (available at www.apple.com/server/documentation/). For information about
choosing a RAID scheme, see “Choosing RAID Schemes for LUNs” on page 44.
Note: You don’t need to use Disk Utility to format arrays or slices for use with Xsan.
The LUNs are labeled and initialized when you add them to a storage pool using Xsan
Admin. After they are labeled, the LUNs can’t be modified using Disk Utility.
Be sure to create arrays of similar size if you plan to combine them into the same
storage pool. For more information, see “Assigning LUNs to Storage Pools” on page 46.
Using the Xsan Admin Application
You use the Xsan Admin application to set up and manage SANs. You can use Xsan
Admin to manage a SAN from any computer that has access to the SAN’s TCP/IP
subnet.
Xsan Admin is installed in /Applications/Server/.
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Installing Just the Xsan Admin Application
Xsan Admin is included when you install the Xsan software on SAN controller and
client computers. You can also install just Xsan Admin on any other computer you want
to use to manage the SAN. For help, see page 55.
Connecting Through a Firewall
If there is a firewall between the SAN and the computer you’re using to run Xsan
Admin, you need to open port 311 in the firewall so Xsan Admin can communicate with
the SAN computers.
Xsan Admin Preferences
Open Xsan Admin and choose Xsan Admin > Preferences to adjust these settings:
 The use of SSL or digital signatures to secure communications
 Listing computers by IP address instead of using DNS to display names
 Smoothing of SAN utilization graphs
 Connection alerts
 SAN status refresh interval
 The amount of log information displayed
Getting Help
Xsan Admin includes onscreen help. Choose Help > Xsan Admin Help, or click the help
button in any dialog or pane where it appears.
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Using the Command Line
If necessary, you can perform many Xsan setup and management tasks from a shell
command prompt. For more information, see Appendix B.
SAN and Volume Setup Summary
You’ll perform the following tasks to set up your first Xsan storage area network. Details
for each task are on the indicated pages.
1 Set up the Fibre Channel network (page 54)
2 Set up the Ethernet network (page 54)
3 Set up SAN users and groups (page 54)
4 Set up LUNs (page 55)
5 Install Xsan software on SAN computers (page 55)
6 Log in to the SAN (page 57)
7 Choose a controller and add clients (page 58)
8 Label and initialize available LUNs (page 61)
9 Create volumes (page 63)
10 Add storage pools to volumes (page 65)
11 Add LUNs to storage pools (page 67)
12 (Optional) Set up status notifications (page 68)
13 (Optional) Assign folders to storage pools (page 69)
14 (Optional) Set user and group quotas (page 71)
15 Start the volumes and mount them on clients (page 73)
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Setting Up an Xsan Volume on a Storage Area Network
Step 1: Set Up the Fibre Channel Network
m Connect controller computers, client computers, and Xserve RAID storage systems to a
Fibre Channel network. Be sure to configure the switch and make the connections so
that you create a Fibre Channel fabric.
For more information, see the guidelines and requirements under “Fibre Channel
Fabric” on page 35.
Step 2: Set Up the Ethernet Network
m Connect controller computers, client computers, and Xserve RAID systems to a private
TCP/IP subnet, or to the same subnet of an intranet.
Follow the guidelines summarized under “Ethernet TCP/IP Network” on page 36.
Step 3: Set Up SAN Users and Groups
m If you already have a centralized directory of users and groups, use the Directory
Access application on each SAN computer to choose that directory for authentication.
If you don’t have a central directory, you can set one up using Workgroup Manager and
the Open Directory service in Mac OS X Server. Otherwise, you need to recreate the
same set of users and groups on each SAN computer.
Important: If you create users and groups individually on each SAN computer, be
sure that each user or group name is assigned the same numeric user ID (UID) or group
ID (GID) on all SAN computers. One way to do this is to create an identical list of users
and groups in the same order on each computer following a fresh install of the
operating system.
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Step 4: Set Up LUNs
m New Xserve RAID systems are usually preconfigured as two RAID 5 arrays that are ready
to use as LUNs.To set up some other configuration of LUNs, use the RAID Admin
application to create RAID arrays or slices on your Xserve RAID systems. For help
choosing other RAID schemes, see “Choosing RAID Schemes for LUNs” on page 44.
Important: If you set up a LUN that is larger than 2 terabytes (TB), be aware that older
clients (those running Xsan on Mac OS X 10.3 Panther or Xsan 1.2 or earlier on
Mac OS X 10.4 Tiger) cannot read these large LUNs. A dialog appears on these older
clients that says the LUN is unreadable. Be sure to click Ignore to dismiss this dialog.
Do not click Format, or information on the corresponding Xsan volume will be lost. If
you use LUNs greater than 2 TB, you should upgrade all SAN clients to Xsan 1.3 or later
on Mac OS X or Mac OS X Server v10.4.
Step 5: Install Xsan Software on Clients and Controllers
Take the Xsan installation disc to each controller and client computer connected to the
SAN and install the Xsan software.
To install the Xsan file system and Xsan Admin application:
m Insert the disc and double-click the Xsan installer icon.
To install just the Xsan file system without Xsan Admin:
m Click Customize on the final installer window and deselect Xsan Admin.
To install just the Xsan Admin application:
m On the Xsan installation disc, open the Admin Tools folder, and double-click
XsanAdmin.pkg.
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To install Xsan on a computer that has no keyboard or monitor:
1 Log in to a computer that does have a keyboard and monitor, and then insert the
Xsan disc.
2 Open the Terminal application (in /Applications/Utilities/).
3 In Terminal, copy the Xsan installer package to the remote computer:
1 Open Xsan Admin on any computer connected to the SAN.
Xsan Admin is in /Applications/Server/.
You can open Xsan Admin on any computer attached to the SAN, or on any remote
computer that can reach the SAN’s TCP/IP subnet.
2 When the login dialog appears, use an administrator account to log in to a SAN
computer that will be used as a controller.
3 Click Setup.
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4 In the Computers pane, type a name for the SAN and click Save.
The SAN name you type appears in the SAN Components list instead of the controller
name or address. To list the controller instead, deselect “Use SAN name in list” in Xsan
Admin Preferences.
Step 7: Set Up Controllers and Clients
All computers on the local network that have Xsan installed are listed in the Computers
pane. In this step you choose at least one computer to act as metadata controller and
set up the others as clients.
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1 In the Computers pane, select a computer in the list.
If the computer you’re looking for is not listed, make sure the Xsan software is installed
on it, that it is connected to the SAN’s Ethernet subnet, and that it is turned on and not
set to sleep.
2 If the Authenticate button appears, click it and type an administrator user name and
password for the computer you are adding to the SAN.
3 Click Edit.
4 Choose whether the computer will function as a controller or a client.
You must choose at least one computer to act as controller for the SAN. Choose from
the Role pop-up menu:
Client: The computer functions as a client only.
Controller: The computer acts as a controller and is also available for use as a client.
There is no controller-only choice. All controllers are also ready to function as clients.
To prevent a controller from being used as a client, restrict user logins on or physical
access to the computer.
5 If the computer is a controller, choose its failover priority.
Choose High for the primary controller or the only controller in the SAN. Choose
Medium or Low for standby controllers.
6 If this computer is a controller, choose the network interface it will use for metadata
communications with other clients and controllers from the “Access the SAN via” popup menu.
7 Type an Xsan software serial number.
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You can find the serial number for a single copy of Xsan on the Xsan installation
disc sleeve. If you’re using individual licenses for each copy of Xsan, make sure each
serial number in the SAN is unique, and leave the “Registered to” and Organization
fields blank.
If you purchased a site-licensed serial number, you can find it on the documentation
you received when you purchased the license.
8 If you’re using a site-licensed serial number, type the registered license holder and
organization in the “Registered to” and Organization fields. Be sure to type these
exactly as they were provided when you purchased the license.
9 Click OK, and then repeat these steps for other computers in the list.
10 When you’re through, click Save.
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Step 8: Label and Initialize LUNs
Next, label and initialize the available LUNs for use with the Xsan file system. Each LUN
represents one of the RAID arrays or slices you set up using RAID Admin.
1 In Xsan Admin, click LUNs in the Setup pane.
Responding storage devices are listed by name and size. You should see one LUN for
each RAID array or slice you created on Xserve RAID systems attached to the SAN’s
Fibre Channel network.
If some newly created LUNs are not listed, click Refresh or wait a moment for them to
appear. If they still don’t appear, quit Xsan Admin, restart the computer, and try again.
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If existing LUNs are not listed, particularly if they are LUNs you have used before as part
of an old Xsan volume, try removing the old label from the LUN. For instructions, see
“Some LUNs Aren’t Listed in Xsan Admin” on page 146.
2 Select a LUN and click Edit. (You can also just double-click the LUN in the list.)
3 Type a label for the LUN.
4 If the LUN is larger than 2 terabytes (TB) and will be part of a volume mounted only on
clients running Xsan 1.3 or 1.4 on Mac OS X v10.4 Tiger, you can select the option “Allow
LUN to exceed 2 TB capacity.”
5 Click OK
6 Repeat for each unlabeled LUN.
7 Click Save to initialize the LUNs.
Now you can organize the LUNs into storage pools and volumes.
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Step 9: Create Volumes
Next, you’ll create the volumes your users will see.
New Volume
button
1 In Xsan Admin, click Storage in the Setup pane.
2 Click the New Volume button (next to the empty list).
3 Type a name for the volume.
Use only uppercase letters (A–Z), lowercase letters (a–z), numbers (0–9), and
underscores ( _ ). Don’t include spaces or hyphens. The maximum length is 70
characters.
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4 Don’t adjust the block allocation size unless you have specific performance tuning
needs.
For more information, see “Choosing Block Allocation Size for a Volume” on page 98.
5 Choose an allocation strategy. This determines the order in which data is written to the
storage pools that make up the volume. You can choose:
 Round Robin: New data is written to the next available storage pool in the volume.
 Fill: Data is stored on the first storage pool until it is full, and then on the next
storage pool.
 Balance: New data is written to the storage pool that has the most free space.
6 If you have Windows clients, choose an ID mapping method.
Note: To use ID mapping, Windows clients must be running StorNext 2.7. Xsan
controllers and clients must be running Xsan 1.3 or later.
 Generate IDs from GUID: Windows clients dynamically generate UIDs and GIDs
based on GUID information in an Active Directory domain.
 Use IDs from LDAP (RFC 2307): Windows clients get UID and GID values from the
uidNumber and gidNumber attributes in Active Directory records.
For more information, see “Mapping Windows User and Group IDs” on page 112.
7 Click OK.
Repeat these steps if you want to create additional volumes.
Now you’re ready to add storage pools to each volume.
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Step 10: Add Storage Pools to the Volumes
New Storage
Pool button
1 Select a volume in the list and click the New Storage Pool button (next to the list).
2 In the storage pool dialog, provide the following information.
 Storage Pool Name: Type a name for the storage pool. If the OK button is disabled
after you type a name, the name is reserved. For a list of reserved names, see “You’re
Unable to Add a Storage Pool” on page 151.
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 Use for: Choose the type of data to store in the storage pool. Journal data is used by
the controller to ensure the integrity of files in the volume. Metadata is file system
information used by the controller. Journal data and metadata are always stored at
least on the first storage pool in a volume. If this is not the first storage pool in the
volume, you can choose “User data only.” To allow only files saved in a folder that has
an affinity for this storage pool, enable “Only data with affinity.”
 Stripe Breadth: Unless you have calculated a different value for performance tuning,
leave this set to the default (256 blocks). Otherwise, change this number to the
amount of data written, in turn, to each LUN in the storage pool. For optimum
performance with Xserve RAID systems, the stripe breadth multiplied by the block
allocation size (which you set for the volume) should equal 1 MB (1,048,576 bytes).
For more information, see “Choosing Stripe Breadth for a Storage Pool” on page 93.
 Multipath Method: If you have two Fibre Channel connections between each client
computer and Xserve RAID system, choose how Xsan uses the connections. Choose
Rotate to have Xsan alternate between the connections for maximum throughput.
Choose Static to have Xsan assign each LUN in the storage pool alternately to one of
the connections when the volume is mounted.
3 Click OK to return to the list.
4 Repeat for each storage pool you need.
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Step 11: Add LUNs to Storage Pools
The final step in preparing storage for the SAN is assigning LUNs to the storage pools
in your SAN volumes:
Click to open a
drawer of unused
LUNs.
1 Select a storage pool in the Storage pane and click Available LUNs.
A drawer opens with a list of all the LUNs you initialized on page 61.
2 Drag LUNs from the drawer to the storage pool.
If a new LUN is larger than the LUNs already in the storage pool, the usable size is
shown next to the LUN in the list.
3 Click Save.
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Step 12: (Optional) Set Up SAN Status Notifications
Xsan can notify you by email or pager when the condition of the SAN changes. If you
don’t want to set up notifications now, you can do it later.
Click to add a
new address.
1 In the Notification pane, click the Add button (+) next to the list to add a contact.
2 Type an email address or the address of a pager text-messaging account, and press
Return.
3 If the entry is for a pager, select the checkbox in the Page column.
4 Choose the conditions that cause a notification to be sent (next to “Notify if”).
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5 If the notification is to be sent to a computer that is not on the local SAN subnet, click
SMTP Info and enter a sender name and the mail server address for the SMTP server
that will relay the email.
6 To verify that notifications are set up correctly, click Send Test Notification.
Step 13: (Optional) Assign Folders to Storage Pools
If you want to force specific files to be stored in a specific storage pool of a volume,
create a folder with an affinity for that storage pool. Then, files that users put in the
folder are stored only on that storage pool.
Click to add a
new folder.
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1 In Xsan Admin, select a volume in the SAN Components list and click Start Volume.
2 With the volume still selected, click Clients.
3 Select the controller you’re connected to and click Mount Read & Write.
4 Click Affinities.
5 If the folder doesn’t already exist, click the Add (+) button next to the list.
6 In the dialog that appears, type a name for the folder, choose the storage pool where
the folder (and all files placed in it) will be stored, and click OK.
If the storage pool you want to use is not listed in the Storage Pool Affinity pop-up
menu, it might not be set to allow user data. To check, select the SAN in the SAN
Components list, click Setup, and click Storage. Then select the storage pool, click the
Edit button, and check which data types are enabled next to Use For.
7 Select the new folder and set permissions (below the list).
To change the owner or group, click the Add (+) button and drag a user or group from
the drawer that appears.
8 Click Save.
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Step 14: (Optional) Set User and Group Quotas
You can set up quotas to control how much space on each SAN volume is used by
each user or group.
Click to add a
new quota.
1 If the volume you want to set the quota for is not already started, select it in the SAN
Components list and click Start Volume.
2 With the volume still selected, click Quotas.
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3 Click the Add (+) button, and then drag a user or group from the drawer to the
quotas list.
If you don’t see the SAN users in the drawer, open Directory Access (in /Applications/
Utilities/) and make sure you’re using the correct directory for user authentication.
4 Select the user or group in the quotas list and adjust their quota settings in the lower
half of the window.
 Soft Quota: The user’s recommended working maximum. The user can exceed this
limit as needed, but only for the length of time specified following “Quota locked
after.”
 Hard Quota: The absolute maximum amount of storage the user’s data can occupy.
 “Quota locked after __”: The length of time the user can exceed his or her soft
quota before it automatically becomes a hard quota.
5 Click Save.
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Step 15: Start the Volumes and Mount Them on Clients
To make a volume available to a user or application on a client computer, you must use
Xsan Admin to start the volume and mount it on the client. Users logged in to client
computers can’t browse for or mount SAN volumes themselves.
1 In Xsan Admin, select each new volume in the SAN Components list and click Start
Volume.
If you already set up affinities or quotas on the volume, the volume is already started.
2 With the volume still selected, click Clients.
3 Select a client computer.
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4 To allow the client to modify files on the volume, click Mount Read & Write.
To prevent the client from modifying the volume, click Mount Read Only.
Shift-click computers to mount on more than one at a time.
An icon for the mounted volume appears in the Finder on each client computer.
If you’re unable to mount volumes on a client, check your Fibre Channel switch
configuration to be sure that the SAN’s clients, controllers, and storage devices are in
the same Fibre Channel zone. If you still have trouble, try shutting down all clients and
controllers, restarting the controller first and then the clients, and mounting again.
Renaming a SAN
SANs are listed by name in the SAN Components list in Xsan Admin. By default, a SAN
is named for the controller you connect to when you set up the SAN. You can change
this name using Xsan Admin.
To change the name of a SAN:
1 Open Xsan Admin (in /Applications/Server/).
2 Select the SAN in the SAN Components list.
If the SAN is not listed under SAN Components, click Connect and log in to the SAN’s
controller.
3 Click Setup, and then click Computers.
4 Type a name in the SAN Name field and click Save.
5 If the new name does not appear in the SAN Components list, choose Xsan Admin >
Preferences and select “Use SAN name in list.”
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Removing a SAN
Follow these steps to take a SAN out of service and remove it from Xsan Admin.
To remove a SAN:
1 Open Xsan Admin (in /Applications/Server/).
2 Unmount the SAN’s volumes from client computers.
Select each of the SAN’s volumes in the SAN Components list, click Clients, select each
client that has the volume mounted, and click Unmount.
3 Stop the SAN’s volumes.
Select each of the SAN’s volumes in the SAN Components list and click Stop Volume.
4 Select the SAN in the SAN Components list and click Remove SAN.
Setting Up Additional SANs
You can use Xsan Admin to set up and manage more than one SAN. To add a new SAN,
connect computers and storage devices to Fibre Channel and Ethernet networks,
identify computers that will act as controllers or clients, organize available storage by
combining Xserve RAID arrays and slices (LUNs) into storage pools and storage pools
into volumes, and mount the resulting volumes on client computers.
If you are setting up a SAN for the first time, see the planning guidelines and more
detailed instructions earlier in this chapter.
To add a SAN:
m Open Xsan Admin, click Add SAN, and log in to a computer you will use as a controller
for the new SAN. Then set up the SAN as described under “SAN and Volume Setup
Summary” on page 53.
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3 Managing SAN Storage
This chapter shows how to expand, modify, check, and repair
SAN storage.
This chapter shows how to:
 Add storage to a SAN (page 78)
 Add LUNs to storage pools (page 80)
 Add storage pools to volumes (page 82)
 Add a volume (page 84)
 Create a folder with an affinity for a particular storage pool (page 86)
 Assign an affinity to a folder within a folder (page 87)
 Remove an affinity (page 89)
 Change storage pool settings (page 90)
 Rename a storage pool (page 91)
 Choose the types of files to store on a storage pool (page 92)
 Set the storage pool stripe breadth (page 92)
 Set the method for choosing a connection (page 94)
 Change volume settings (page 95)
 Rename a volume (page 96)
3
77
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 Set the block allocation size (page 97)
 Set the storage allocation strategy (page 99)
 Enable or disable access control lists (page 100)
 Set the Windows ID mapping method (page 101)
 Check volume fragmentation (page 101)
 Defragment a volume (page 102)
 Check a volume (page 103)
 Repair a volume (page 104)
Adding Storage
There are several ways you can add storage to a SAN:
 Add RAID arrays (LUNs) to existing storage pools
 Add storage pools to existing volumes
 Add new volumes
The first option, adding LUNs to a storage pool, increases available storage and can
improve the performance of the SAN because it increases the number of RAID
controllers and data paths between clients and storage. You’ll need to stop the volume
and unmount it from clients before you add LUNs to any of its storage pools.
Note: You can’t add LUNs to an existing storage pool that is being used to store journal
data or metadata.
The second option, adding a storage pool to a volume, also increases available storage,
and also requires you to stop the volume and unmount it from clients.
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The third option creates a new volume that must be explicitly mounted on client
computers. Clients must then choose to save new files and folders on the new volume,
or copy existing items there, so this option is more likely to disrupt user workflow.
Restoring the Previous Volume Configuration After Changes
If you have trouble with a volume after expanding it, you can restore its previous
configuration so it can be used until you solve the problem. See “You’re Unable to
Restart a Volume After Adding LUNs or Storage Pools” on page 145.
About Rearranging Fibre Channel Connections
If, while expanding or reconfiguring your SAN, you break a Fibre Channel connection
between an Xsan client and a mounted volume for more than one minute, the volume
is unmounted from the client in a way that can cause problems with applications
running on the client and make the volume difficult to remount. To avoid this,
unmount the volume before you disconnect the client.
Important: If you need to disconnect a Fibre Channel cable for more than a minute,
you should first unmount all Xsan volumes from all controllers and clients on the SAN,
and then either shut down all computers connected to the SAN or disconnect all of
their Fibre Channel cables.
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Adding LUNs to a Storage Pool
You can increase the capacity of a SAN volume by adding LUNs (RAID arrays or array
slices) to a storage pool that belongs to the volume.
Choosing Compatible LUNs
Add LUNs that are similar in performance and capacity to the LUNs already in the
storage pool. Mixing LUNs of different sizes or speeds in the same storage pool wastes
capacity and can degrade performance. If you’re adding a LUN to an existing storage
pool, the LUN must be at least as large as the other LUNs in the pool.
Note: A storage pool can’t contain more than 32 LUNs, the total number of LUNs in a
volume can’t be greater than 512, and you can’t add LUNs to a storage pool that
contains journal data or metadata.
To add a LUN to a storage pool:
1 Connect the new LUN to the SAN’s Fibre Channel and Ethernet networks.
2 Use RAID Admin to create the RAID array or slice. For help, see Using RAID Admin 1.2
and Disk Utility (available at www.apple.com/server/documentation/) or look in the
RAID Admin onscreen help.
Note: Don’t use Disk Utility to format the new array. You’ll use Xsan Admin to format
the array for Xsan in step 6.
3 Open Xsan Admin, select the volume in the SAN Components list, click Clients, and
unmount the volume from all clients and controllers.
4 Stop the volume.
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Important: If you forget to unmount the volume (in step 3) before you stop it, be sure
to click Disconnect in the “server no longer available” alert that appears on SAN
computers.
5 Select the SAN in the SAN Components list, click Setup, and then click LUNs.
6 Select the new array or slice in the list of available LUNs and click Edit.
7 In the dialog that appears, type a label for the LUN.
The label can’t contain spaces. Only SAN administrators, not users, will see this label.
8 Click OK, and click Save.
9 Click Storage, and then click Available LUNs.
10 Drag the new LUN to make it the last LUN in the storage pool and click Save.
If you’re adding the LUN to an existing storage pool, it must be at least as large as the
other LUNs in the pool. If the storage pool is new and you’re adding LUNs of different
sizes, the usable size is shown next to the LUN in the list.
11 Start the volume.
12 Select the volume in the SAN Components list, click Clients, and remount the volume
on each client that had it mounted.
Note: To have an existing file redistributed across all of the LUNs in the storage pool
(including the LUN you just added), you must make a new copy of the file. If you are
adding LUNs to speed up access to a file, be sure to duplicate the file so a new copy is
distributed across all available LUNs.
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From the Command Line
You can also add LUNs to a storage pool by modifying the associated volume
configuration file and using the cvlabel command in Terminal. For more information,
see the cvfs_config and cvlabel man pages or “The Configuration Files” on
page 181 and “Labeling, Listing, and Unlabeling LUNs (cvlabel)” on page 172.
Adding a Storage Pool to a Volume
You can add free space to a SAN volume by adding a storage pool to the volume.
Note: A volume can’t contain more than 512 storage pools.
To add a storage pool:
1 Prepare the LUNs you’ll use to create the storage pool.
2 Open Xsan Admin, select the volume in the SAN Components list, click Clients, and
unmount the volume from all clients and controllers.
3 Stop the volume.
Important: If you forget to unmount the volume (in step 2) before you stop it, be sure
to click Disconnect in the “server no longer available” alert that appears on SAN
computers.
4 Select the SAN in the SAN Components list, click Setup, and then click Storage.
5 Select the volume you’re expanding, and then click the Add Storage Pool button (next
to the list).
6 In the dialog that appears, specify:
 Storage Pool Name: Type a name for the storage pool. If the OK button is disabled
when you finish typing the name, the name is reserved; try another. For a list of
reserved names, see Chapter 7.
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 Use for: Choose the types of data that can be stored on the storage pool.
 Stripe Breadth: Specify how much data is written to or read from each LUN in the
storage pool before moving to the next LUN. This value can affect performance.
If you’re not sure what value to use, use the default (256 blocks) or see “Choosing
Stripe Breadth for a Storage Pool” on page 93.
 Multipath Method: Choose Rotate to have Xsan alternate between the connections
for maximum throughput. Choose Static to have Xsan assign each LUN in the storage
pool alternately to one of the connections when the volume is mounted.
7 Click OK.
8 Click Available LUNs, drag LUNs to the storage pool, and click Save.
9 Start the volume.
10 Select the volume in the SAN Components list, click Clients, and remount the volume
on each client that had it mounted.
From the Command Line
You can also add a storage pool by modifying the associated volume configuration file
in Terminal. For more information, see the cvfs_config man page or “The
Configuration Files” on page 181.
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Adding a Volume to a SAN
A single Xsan SAN can provide multiple shared volumes.
1 Open Xsan Admin and select the SAN in the SAN Components list.
2 Click Setup, and then click Storage.
3 Click the Add Volume button next to the list.
4 In the dialog that appears, provide the following information and then click OK.
 Volume Name: Type a name for the volume. Use only uppercase letters (A–Z),
lowercase letters (a–z), numbers (0–9), or underscores ( _ ). Don’t include spaces or
hyphens. The maximum length is 70 characters.
 Block Allocation Size: If you’re not sure what value to use, use the default (4 KB) or
see “Choosing Block Allocation Size for a Volume” on page 98.
 Allocation Strategy: Choose how storage for files is allocated among the storage
pools that belong to the volume. If you choose Round Robin, each new request for
space is assigned to the next available storage pool in turn. If you choose Fill, all
space is allocated on the first storage pool until it is full, then on the second storage
pool, and so on. If you choose Balance, space is allocated on the storage pool that
has the most free space.
 Access Control Lists: Leave this enabled if you want to use access control lists in
Workgroup Manager to control access to the volume and its contents.
 Windows ID Mapping: If you will have Windows clients on your SAN, choose how
they map user and group information to the Xsan-compatible user IDs and group IDs
they need in order to access this volume. For more information, see “Mapping
Windows User and Group IDs” on page 112.
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5 Select the new volume and click the Add Storage Pool button. In the dialog that
appears, provide the following information, and then click OK.
 Storage Pool Name: Type a name for the storage pool. If the OK button is disabled
when you finish typing the name, the name is reserved; try another. For a list of
reserved names, see Chapter 7.
 Use for: Choose the types of data that can be stored on the storage pool.
 Stripe Breadth: Specify how much data is written to or read from each LUN in the
storage pool before moving to the next LUN. This value can affect performance.
If you’re not sure what value to use, use the default (256 blocks) or see “Choosing
Stripe Breadth for a Storage Pool” on page 93.
 Multipath Method: Choose Rotate to have Xsan alternate between the connections
for maximum throughput. Choose Static to have Xsan assign each LUN in the storage
pool alternately to one of the connections when the volume is mounted.
Repeat to add other storage pools.
6 Click Available LUNs, drag LUNs to the storage pool.
7 Click Save.
From the Command Line
You can also add a volume by setting up a configuration file. For more information, see
the
cvfs_config man page or “The Configuration Files” on page 181.
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Assigning a Storage Pool Affinity to a Folder
You can set up an affinity between a folder and a storage pool so that files saved in the
folder are stored only on the specified storage pool.
When you set up storage pools, you group devices with similar performance, capacity,
and data protection schemes. Depending on the devices and the protection schemes
you choose for them, you might end up with some storage pools that are larger, faster,
or better protected than others. Using affinities, you can make sure that an application
or task that needs speed or extra protection stores its files on a suitable storage pool.
Using Xsan Admin, you can assign an affinity to an existing top-level folder or create a
new top-level folder with an affinity. To assign an affinity to a folder within another
folder, you must use a command in Terminal; see “Assigning an Affinity to a Folder
Within a Folder” on page 87.
To assign a storage pool affinity to a folder:
1 Open Xsan Admin and select the volume that contains the storage pool.
2 If the volume is not started and mounted on the controller, start and mount it.
To start the volume, select it and click Start Volume. To mount the volume, select it,
click Clients, select the controller, and click Mount Read & Write.
3 With the volume still selected, click Affinities.
4 If the folder doesn’t already exist, click the Add button (+) next to the folder list and
type a name for the folder.
If the folder already exists, select it and click the Edit button.
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5 Choose the storage pool (where the folder’s contents will be stored) from the Storage
Pool Affinity pop-up menu in the dialog that appears.
If the storage pool you want to use is not listed in the Storage Pool Affinity pop-up
menu, it might not be set to allow user data. To check, select the SAN in the SAN
Components list on the left, click Setup, and click Storage. Then select the storage pool,
click the Edit button, and check which data types are enabled next to Use For.
6 Click OK, and then click Save.
From the Command Line
You can also assign an affinity to a folder using the cvmkdir command in Terminal.
For more information, see the cvmkdir man page or “Assigning an Affinity to a Folder
Within a Folder” on page 87.
Assigning an Affinity to a Folder Within a Folder
You can use Xsan Admin to assign an affinity to a folder at the top, or root, level of a
volume, but to assign an affinity to a folder that is inside another folder you need to
use the cvmkdir command-line tool.
To assign a storage pool affinity to a folder within a folder:
1 Open Terminal (in /Applications/Utilities/).
2 If you are not working at a SAN controller, use SSH to log in to the controller remotely:
$ ssh user@computer
where user is an administrator user on the controller computer and computer is the
controller’s name or IP address.
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3 In Terminal, type
$ sudo cvmkdir -k affinity path
where affinity is the affinity name of a storage pool in the volume and path is the
full path to the folder on the volume. If the name of the storage pool is 8 characters or
less, you can use the storage pool name for the affinity name. If the storage pool name
is longer than 8 characters, you must use the affinity name instead of the storage pool
name.
To see a storage pool’s affinity name, use the cat command in Terminal or use a text
editor such as TextEdit to look at the configuration file for the volume on the controller:
/Library/Filesystems/Xsan/config/<volume>.cfg
The affinity name for the storage pool is listed in this file next to the Affinity keyword in
the block of parameters for the storage pool (called a “stripe group” in the
configuration file). Look in the section of the file that defines stripe groups.
For example, to assign an affinity for the storage pool “pool1” to folder “gina audio”
which is inside the folder “projects” on the volume “audio,” you would type
The way you remove an affinity depends on whether the affected folder is at the top
level of the volume or inside another folder.
To remove a storage pool affinity from a folder:
1 If the folder is at the top level of the volume (not within another folder), open Xsan
Admin, select the volume, click Affinities, double-click the folder and choose Any
Storage Pool from the Storage Pool Affinity pop-up menu.
If the folder is inside another folder on the volume, continue with the next step.
2 Open Terminal (in /Applications/Utilities/).
3 If you are not working at a SAN controller, use SSH to log in to the controller remotely:
$ ssh user@computer
where user is an administrator user on the controller computer and computer is the
controller’s name or IP address.
4 In Terminal, type
$ sudo cvmkdir -k ““ path
where path is the full path to the folder on the volume.
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Changing Storage Pool Settings
The best way to set up a SAN is to plan its organization carefully before you set it up,
including settings for the storage pools that make up its volumes. You can change
some storage pool settings on an existing SAN, but other changes require the
associated volume to be reinitialized.
Edit button
To view or change storage pool settings:
m Select the SAN in the SAN Components list, click Setup, and click Storage. Then select a
storage pool and click the Edit button (or double-click a storage pool).
See the following pages for information about changing specific storage pool settings.
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Renaming a Storage Pool
You can rename a storage pool, but doing so erases all data on the storage pool and
the volume it belongs to.
Warning: When you rename a storage pool, all data on the storage pool and the
volume to which it belongs is lost.
To rename a storage pool:
1 Unmount the associated volume from all clients.
In Xsan Admin, select the volume, click Clients, select clients in the list, and click
Unmount.
2 Stop the associated volume.
With the volume still selected, click Stop Volume.
3 Rename the storage pool.
Select the SAN, click Setup, click Storage, and double-click the storage pool in the list.
Type the new name and click OK.
4 Click Save.
From the Command Line
You can also rename a storage pool by modifying the associated volume configuration
file in Terminal. For more information, see the
Configuration Files” on page 181.
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cvfs_config man page or “The
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Choosing the Types of Files Stored on a Storage Pool
You can limit the files that are stored on a particular storage pool to volume journal
data and metadata, user data, user data with an affinity for that storage pool, or a
combination of these.
Warning: When you change the data type of a storage pool, all data on the storage
pool and the volume to which it belongs is lost.
Journal data and metadata are always stored on the first storage pool in a volume.
To choose the data types for a storage pool:
1 In Xsan Admin, select the SAN the storage pool belongs to, click Setup, and click
Storage.
2 Double-click the storage pool in the list.
3 Next to “Use for,” choose the data types to store on the storage pool.
4 Click OK, and then click Save.
Setting Storage Pool Stripe Breadth
The default stripe breadth value (256 file system blocks) is adequate for storage pools
in most SAN volumes. However, you can adjust this value along with the file system
block allocation size to tune SAN performance for special applications. For help
choosing a stripe breadth, see “Choosing Stripe Breadth for a Storage Pool,” below.
Warning: When you change a storage pool’s stripe breadth, all data on the storage
pool and the volume to which it belongs is lost.
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To set the stripe breadth:
1 In Xsan Admin, select the SAN that the storage pool belongs to, click Setup, and click
Storage.
2 Double-click the storage pool in the list.
3 Next to Stripe Breadth, type the new value.
4 Click OK, and then click Save.
Choosing Stripe Breadth for a Storage Pool
Xsan uses the storage pool stripe breadth and volume block allocation size together to
decide how to write data to a volume. For most SANs, the default values for storage
pool stripe breadth and volume block allocation size result in good performance.
However, in some cases you might be able to improve read and write performance by
adjusting these values to suit a specific application.
The stripe breadth of a storage pool is the number of file allocation blocks that are
written to a LUN in the pool before moving to the next LUN. To choose an efficient
stripe breadth, you need to consider two other factors:
 The most efficient data transfer size of the LUN storage device (1 MB for the
combination of Mac OS X or Mac OS X Server and Xserve RAID systems)
 The size of the data blocks written and read by the critical application that uses the
volume (as reflected in the block allocation size for the volume)
Knowing these values, choose a stripe breadth using this formula:
stripe breadth (in blocks) = transfer size (in bytes) / block allocation size (in bytes)
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For Xserve RAID systems, which have an optimal transfer size of 1 MB, this becomes:
stripe breadth = 1048576 / block allocation size
If, for example, you are using an application such as Final Cut Pro to move large
amounts of video data, choose the largest block allocation size (512KB) and use the
equation to find the stripe breadth of 2 blocks. Then, Xsan writes 1 MB of data (two
512KB blocks), in turn, to each LUN in your video storage pool.
Setting the Selection Method for Multiple Connections
If there is more than one Fibre Channel connection to the LUNs in a storage pool, you
can choose whether Xsan alternates between connections for each write or statically
assigns each LUN in the volume to a connection at volume mount time. This is called
the “multipath method.”
To change the multipath method:
1 In Xsan Admin, select the SAN that the storage pool belongs to, click Setup, and click
Storage.
2 Double-click the storage pool in the list.
3 Choose a value from the Multipath Method pop-up menu.
 Static: Xsan assigns each LUN in a storage pool to one of the connections when the
volume is mounted.
 Rotate: Xsan switches to a different connection each time it writes data to the
storage pool. This can improve performance.
4 Click OK, and then click Save.
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From the Command Line
You can also set the multipath method using the cvadmin multipath command in
Terminal. For more information, see the cvadmin man page or “Viewing or Changing
Volume and Storage Pool Settings (cvadmin)” on page 164.
Changing Volume Settings
You can change some settings for an existing volume, but other changes require the
volume to be re-initialized (you’ll see a warning for these cases).
Edit button
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To view or change volume settings:
m Select the SAN in the SAN Components list, click Setup, and click Storage. Then select a
volume and click the Edit button (or double-click a volume).
See the following pages for information about changing specific volume settings.
Renaming a Volume
You must use Xsan Admin to change the name users see when the volume is mounted
on their computers. You can’t rename Xsan volumes using the Finder.
Warning: Renaming a volume causes all data on the volume to be lost.
To rename a volume:
1 Unmount the volume from clients.
In Xsan Admin, select the volume and click Clients. Then select clients and click
Unmount.
2 Stop the volume.
In Xsan Admin, select the volume and click Stop Volume.
3 Rename the volume.
In Xsan Admin, select the SAN that the volume belongs to, click Setup, and click
Storage. Then double-click the volume, type a new name in the Volume Name field,
click OK, and click Save.
Use only uppercase letters (A–Z), lowercase letters (a–z), numbers (0–9), or underscores
( _ ). Don’t include spaces or hyphens. The maximum length is 70 characters.
4 Start the volume.
Select the volume in the SAN Components list and click Start Volume.
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5 Mount the volume on clients.
Select the volume and click Clients. Select clients and click Mount.
Setting the Block Allocation Size
The default file system block allocation size (4 KB) is adequate for most volumes.
However, you can adjust this value along with the stripe breadth of the volume’s
storage pools to tune performance for special applications. For help choosing a block
allocation size, see “Choosing Block Allocation Size for a Volume,” below.
Warning: When you change a volume’s block allocation size, all data on the volume
is lost.
To set the block allocation size:
1 In Xsan Admin, select the volume in the SAN Components list, click Clients, and
unmount the volume from all clients and controllers.
2 Click Stop Volume.
Important: If you forget to unmount the volume (in step 1) before you stop it, be sure
to click Disconnect in the “server no longer available” alert that appears on any
computer that has the volume mounted.
3 Select the SAN, click Setup, and then click Storage.
4 Double-click the volume in the list.
5 Use the up and down arrows to choose a new value for Block Allocation Size.
6 Click OK, and then click Save.
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Choosing Block Allocation Size for a Volume
Xsan uses the volume block allocation size and storage pool stripe breadth together to
decide how to write data to a volume. For most SANs, the default values for volume
block allocation size and storage pool stripe breadth result in good performance.
However, in some cases you might be able to improve read and write performance by
adjusting these values to suit a specific application.
If the critical application that uses the volume reads and writes small blocks of data,
you might improve performance by choosing a correspondingly small allocation block
size. If, for example, the application reads and writes 16 KB blocks of data, you can try
adjusting the block allocation size to 16 KB. Then calculate the best corresponding
stripe breadth for the volume’s storage pools using this formula:
For Xserve RAID systems, which have an optimal transfer size of 1 MB when used in
conjunction with Mac OS X or Mac OS X Server, this becomes:
stripe breadth = 1048576 / block allocation size
For the block allocation size of 16 KB in the example, solving the equation (1048576/
16384) gives a stripe breadth of 64.
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Setting the Volume Allocation Strategy
You can set the allocation strategy for a volume to determine the order in which data is
written to the volume’s storage pools.
To set the allocation strategy:
1 In Xsan Admin, select the volume in the SAN Components list, click Clients, and
unmount the volume from all clients and controllers.
2 Click Stop Volume.
Important: If you forget to unmount the volume (in step 1) before you stop it, be sure
to click Disconnect in the “server no longer available” alert that appears on any
computer that has the volume mounted.
3 Select the SAN that the volume belongs to, click Setup, and click Storage.
4 Double-click the volume in the list.
5 Choose a value from the Allocation Strategy pop-up menu.
 Round Robin: New data is written to the next available storage pool in the volume.
 Fill: All data is stored on the first storage pool until it is full, then on the next storage
pool, and so on.
 Balance: New data is written to the storage pool that has the most free space.
6 Click OK, and then click Save.
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Enabling or Disabling Access Control Lists
You can use Xsan Admin to specify whether the Xsan file system uses access control
lists (ACLs) on a volume.
To use ACLs, your SAN controller must be running Xsan 1.4. Only Xsan 1.4 clients and
Windows StorNext clients recognize ACLs. (ACLs on Xsan volumes are ignored by UNIX
clients as well as clients running Xsan 1.3 or earlier.) If you have a mix of Windows
clients and Xsan clients, they must all be bound to the same directory domain, whether
provided by Open Directory configured as a Primary Domain Controller (PDC), by
Windows Active Directory, or by Windows NT PDC.
Note: If you enable ACLs but your SAN includes clients that don’t support them, don’t
use those clients to change ownership information or inconsistencies might result.
To enable or disable ACLs:
1 In Xsan Admin, select the volume in the SAN Components list, click Clients, and
unmount the volume from all clients and controllers.
2 Click Stop Volume.
Important: If you forget to unmount the volume (in step 1) before you stop it, be sure
to click Disconnect in the “server no longer available” alert that appears on any
computer that has the volume mounted.
3 Select the SAN that the volume belongs to, click Setup, and click Storage.
4 Double-click the volume in the list.
5 Set or clear the checkbox next to Access Control Lists and click OK.
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