Apple XSAN 1.0 Getting Started
Xsan
Getting Started
Includes instructions for setting up shared
volumes on a storage area network
Apple Computer, Inc.
© 2004 Apple Computer, Inc. All rights reserved.
The owner or authorized user of a valid copy of Xsan
software may reproduce this publication for the purpose
of learning to use such software. No part of this
publication may be reproduced or transmitted for
commercial purposes, such as selling copies of this
publication or for providing paid for support services.
The Apple logo is a trademark of Apple Computer, Inc.,
registered in the U.S. and other countries. Use of the
“keyboard” Apple logo (Option-Shift-K) for commercial
purposes without the prior written consent of Apple
may constitute trademark infringement and unfair
competition in violation of federal and state laws.
Apple, the Apple logo, Mac, Macintosh, Mac OS, Power
Mac, and Xserve are trademarks of Apple Computer, Inc.,
registered in the U.S. and other countries. Finder and
Xsan are trademarks of Apple Computer, Inc.
UNIX is a registered trademark in the United States and
other countries, licensed exclusively through
X/Open Company, Ltd.
StorNext and ADIC are registered trademarks of
Advanced Digital Information Corporation.
034-2652-A/08-27-04
3
Contents
Preface 5 About This Guide
5
Using this Guide
5
For More Information
Chapter 1 7 Introduction to Xsan
7
What Is Xsan?
8
Xsan and Storage Area Networks
9
Shared SAN Volumes
9
Controllers and Clients
9
SAN Connections
10
How Xsan Storage Is Organized
10
11
11
12
13
13
13
13
14
LUNs (RAID Arrays)
Storage Pools
Volumes
Folders With Affinities
How Xsan Utilizes Available Storage
Metadata and Journal Data
Striping at a Higher Level
Security
Expanding Storage
Chapter 2 15 Before You Begin
15
Hardware and Software Requirements
15
16
16
17
17
17
18
19
24
24
Supported Computers
Supported Storage Devices
Fibre Channel Fabric
Ethernet TCP/IP Network
Directory Services
Outgoing Mail Service
Planning Your SAN Volumes
Planning Considerations and Guidelines
Connecting Computers and Storage Devices
Preparing LUNs (RAID Arrays and Slices)
3
25
Using the Xsan Admin Application
25
25
25
25
Installing Xsan Admin Separately
Connecting Through a Firewall
Getting Help
Using the Command Line
Chapter 3 27 Setting Up a SAN Volume
27
Setup Summary
28
Setting Up an Xsan Storage Area Network
Appendix 37 Working With StorNext Clients and Controllers
37
Compatible Software Versions
37
Licensing
38
Adding Macintosh Clients to a StorNext SAN
39
Using Xsan Controllers With StorNext Clients
Glossary 41
4
Contents
About This Guide
This guide shows how to set up your first Xsan volumes
on a storage area network.
Use the instructions in this guide to plan and set up shared volumes of storage on a
storage area network (SAN).
Using this Guide
For an overview of Xsan and storage area networks, read Chapter 1.
To review hardware, software, and network requirements, and to see tips for planning
your SAN volumes, read Chapter 2.
For step-by-step instructions for setting up a SAN volume, read Chapter 3.
If you want to use Macintosh Xsan clients or controllers together with existing ADIC
StorNext File System clients or controllers, see the appendix.
Preface
For More Information
The
Xsan Administrator’s Guide
volumes, including problem-solving tips and command-line alternatives for common
tasks. You can find the administrator’s guide:
•
On the Xsan installer disc
In the folder /Library/Documentation/Xsan on any computer where Xsan is installed
•
•
At www.apple.com/server/documentation
contains additional information about managing Xsan
5
1
Introduction to Xsan
1
This chapter gives you an overview of Xsan and how you
can use it to provide fast, shared storage on a storage
area network (SAN).
If you want to set up an Xsan volume on a storage area network right now, skip to
Chapter 2, “Before You Begin,” on page 15.
What Is Xsan?
Xsan is a storage area network file system and a management application (Xsan Admin)
you can use to provide users or applications on client computers with shared highspeed access to expandable storage.
Fibre
Channel
Volumes
SAN vol
Xsan lets you
combine RAID arrays
into volumes clients
use like local disks.
Storage
pools
RAID
arrays (LUNs)
7
Xsan and 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.
Clients
Ethernet - TCP/IP
(Private)
Ethernet - TCP/IP
(Public)
Metadata
controller
Fibre
Channel switch
Standby
controller
Xserve RAID
storage
Intranet/
Internet
8 Chapter 1
Introduction to Xsan
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 10.
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 can add more than one controller to a SAN, as shown in the
illustration on page 8. If the primary controller fails, the standby controller takes over.
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.
A SAN client might be an individual user’s Mac OS X computer or a server running
Mac OS X Server. 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.
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.
Metadata Over Ethernet
To eliminate unnecessary traffic on the Fibre Channel connections, controllers and
clients use an Ethernet network to exchange file system metadata. The Xsan Admin
application also uses the Ethernet connection to let you manage the SAN. To prevent
other network traffic from interfering with metadata transfers, you can use two
separate Ethernet networks; one private for the SAN, and the other public.
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.
Chapter 1
Introduction to Xsan
9
How Xsan Storage Is Organized
Users work with 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 individual
drive modules in Xserve RAID systems is combined into a volume that users see as a
large local disk.
Shared SAN
volume
Faster
RAID 0
array
Safer
LUN LUN
RAID 5
RAID 5
array
array
LUN LUN
RAID 5
RAID 5
array
array
LUN LUN
RAID 0
RAID 0
array
Affinity Affinity
Storage pool Storage pool
(Striping) (Striping)
LUN LUN
RAID 0
array
array
The following paragraphs describe these storage elements and how you organize them
to create shared Xsan volumes.
LUNs (RAID Arrays)
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 whenever you use RAID Admin 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 Fibre Channel network as a LUN, and if you slice the array into two or more slices,
each slice appears as a separate LUN.
10 Chapter 1
Introduction to Xsan
One of your first tasks when setting 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 20.
For example, the illustration on page 10 shows four Xserve RAID systems hosting two
arrays each. 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.
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 include 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 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 12.
As an example, the illustration on page 10 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.
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 example illustrated on page 10, 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.
Chapter 1
Introduction to Xsan
11
The following screen image shows how LUNs, storage pools, and volumes appear as
you organize them in the Xsan Admin application. This example shows a SAN named
“Test SAN” with a single shared volume named “SanVol.” Storage for the volume is
provided by two storage pools, “Pool1” and “Pool2,” each based on a single LUN. Each
of the LUNs is a 3-disk RAID 5 array on an Xserve RAID using 115 GB drive modules.
SAN
Volume
Storage pool
LUN
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 10, 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.
12 Chapter 1
Introduction to Xsan
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.
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.
Security
As 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 also control user access to folders on a volume by specifying owner, group,
and general access permissions as you would in the Finder.
You can also set up zones in the underlying Fibre Channel network to segregate users
and volumes.
Chapter 1
Introduction to Xsan
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