LSI MegaRAID Express 500 User Manual
MegaRAID® Express 500
Hardware Guide
MAN-475
6/13/2001
© Copyright 2001 LSI Logic Corporation
All rights reserved.
LSI Logic Corporation
6145-D Northbelt Parkway
Norcross, GA 30071
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Revision History
4/14/00 Initial release.
4/11/01 Corrected RAID 0 graphic, and Array Configuration Planner table.
6/13/01 Make corrections, such as cache size (16 MB is smallest option), and the number of physical disk drives
supported at various RAID levels.
MegaRAID Express500 Hardware Guide
ii
Table of Contents
1 Overview .................................................. 1
Single Ended and Differential SCSI Buses....................... 2
Maximum Cable Length for SCSI Standards....................2
Documentation..................................................................3
MegaRAID Express 500 Block Diagram..........................4
2 Introduction to RAID................................ 5
RAID Benefits.................................................................. 5
In This Chapter................................................................. 6
MegaRAID Express 500 – Host-Based RAID Solution ... 7
RAID Overview................................................................ 8
Fault Tolerance................................................................. 8
Consistency Check............................................................ 8
Disk Rebuild..................................................................... 9
Hot Spares ......................................................................10
Hot Swap ........................................................................ 10
Parity ..............................................................................11
Disk Striping................................................................... 12
Disk Mirroring................................................................ 13
Disk Spanning.................................................................14
Logical Drive.................................................................. 15
Logical Drive States .......................................................15
SCSI Drive States ........................................................... 15
Disk Array Types............................................................16
Enclosure Management................................................... 16
3 RAID Levels............................................ 17
Selecting a RAID Level.................................................. 18
RAID 0 ........................................................................... 19
RAID 1 ........................................................................... 20
RAID 3 ........................................................................... 21
RAID 5 ........................................................................... 23
RAID 10 ......................................................................... 24
RAID 30 ......................................................................... 25
RAID 50 ......................................................................... 26
Preface
iii
Table of Contents,
Continued
4 Features ................................................. 27
Hardware Requirements .................................................28
Configuration Features ................................................... 28
Hardware Architecture Features..................................... 29
Array Performance Features ........................................... 29
RAID Management Features ..........................................30
Fault Tolerance Features.................................................30
Software Utilities............................................................ 31
Operating System Software Drivers................................31
MegaRAID Express 500 Specifications .........................32
PCI Bridge/CPU ............................................................. 32
Cache Memory................................................................33
MegaRAID BIOS ...........................................................33
Onboard Speaker ............................................................ 33
Serial Port ....................................................................... 33
SCSI Bus ........................................................................34
SCSI Connectors.............................................................34
SCSI Termination........................................................... 34
SCSI Firmware ...............................................................34
RAID Management......................................................... 35
Fault-Tolerance Features ................................................ 35
Compatibility.................................................................. 36
Summary.........................................................................36
5 Configuring MegaRAID Express 500 ... 37
Configuring SCSI Physical Drives..................................37
Current Configuration..................................................... 38
Logical Drive Configuration........................................... 38
Physical Device Layout ..................................................40
Configuring Arrays......................................................... 42
Configuration Strategies ................................................. 43
Assigning RAID Levels.................................................. 45
Configuring Logical Drives ............................................45
Optimizing Data Storage ................................................ 46
Planning the Array Configuration................................... 46
Array Configuration Planner........................................... 47
MegaRAID Express500 Hardware Guide
iv
Table of Contents,
Continued
6 Hardware Installation ............................ 49
Checklist......................................................................... 49
Installation Steps.............................................................50
Step 1 Unpack.................................................................51
Step 2 Power Down ........................................................ 51
Step 3 Configure Motherboard....................................... 51
Step 4 Install Cache Memory..........................................52
Step 5 Set Jumpers.......................................................... 53
MegaRAID Express 500 Card Layout............................ 53
Step 6 Set Termination ................................................... 56
SCSI Termination........................................................... 57
Step 7 Install MegaRAID Express 500........................... 60
Step 8 Connect SCSI Cables...........................................61
Step 9 Set Target IDs...................................................... 62
Device Identification on MegaRAID Express 500 .........63
Step 10 Power Up........................................................... 64
Step 11 Run MegaRAID BIOS Setup.............................64
Step 12 Install the Operating System Driver................... 65
Summary.........................................................................66
7 Cluster Installation and Configuration 67
Software Requirements................................................... 67
Hardware Requirements .................................................68
Installation and Configuration ........................................69
Driver Installation Instructions under Microsoft
Windows 2000 Advanced Server ...................................70
Network Requirements ................................................... 75
Shared Disk Requirements.............................................. 75
Cluster Installation.......................................................... 76
Installing the Windows 2000 Operating System............. 77
Setting Up Networks.......................................................77
Configuring the Cluster Node Network Adapter ............ 79
Configuring the Public Network Adapter ....................... 80
Verifying Connectivity and Name Resolution................ 80
Verifying Domain Membership...................................... 81
Setting Up a Cluster User Account................................. 82
Setting Up Shared Disks................................................. 83
Configuring Shared Disks............................................... 84
Assigning Drive Letters .................................................. 84
Verifying Disk Access and Functionality .......................85
Cluster Service Software Installation.............................. 86
Configuring Cluster Disks ..............................................89
Validating the Cluster Installation ..................................95
Configuring the Second Node......................................... 95
Verify Installation........................................................... 96
SCSI Drive Installations .................................................97
Configuring the SCSI Devices........................................ 97
Terminating the Shared SCSI Bus.................................. 97
Preface
v
Table of Contents,
Continued
8 Troubleshooting .................................... 99
BIOS Boot Error Messages .......................................... 101
Other BIOS Error Messages......................................... 103
DOS ASPI Driver Error Messages ............................... 104
Other Potential Problems.............................................. 105
A SCSI Cables and Connectors ............. 107
SCSI Connectors...........................................................107
68-Pin High Density SCSI Internal Connector ............. 107
High-Density 68-Pin SCSI Connector Pinout............... 113
68-Pin SCSI Connector Pinout, Continued................... 114
68-Pin Connector Pinout for LVD SCSI ...................... 115
B Audible Warnings ................................ 117
C Cluster Configuration with a Crossover Cable...119
Solution.........................................................................120
Glossary.......................................................... 121
Index................................................................ 131
MegaRAID Express500 Hardware Guide
vi
Preface
The MegaRAID Express 500 PCI RAID Controller supports all single ended and low-voltage
differential (LVD) SCSI devices on a 160M Ultra and Wide SCSI channel with data transfer rates
up to 160 MB/s (Megabytes per second). This manual describes MegaRAID Express 500.
Limited Warranty
Limitations of Liability
The buyer agrees if this product proves to be defective, that LSI Logic is obligated only to repair or
replace this product at LSI Logic’s discretion according to the terms and conditions of the warranty
registration card that accompanies this product. LSI Logic shall not be liable in tort or contract for
any loss or damage, direct, incidental or consequential resulting from the use of this product. Please
see the Warranty Registration Card shipped with this product for full warranty details.
any kind whatsoever, whether direct, indirect, incidental, or consequential (whether arising from
the design or use of this product or the support materials provided with the product). No action or
proceeding against LSI Logic Corporation may be commenced more than two years after the
delivery of product to Licensee of Licensed Software.
Licensee agrees to defend and indemnify LSI Logic Corporation from any and all claims, suits, and
liabilities (including attorney’s fees) arising out of or resulting from any actual or alleged act or
omission on the part of Licensee, its authorized third parties, employees, or agents, in connection
with the distribution of Licensed Software to end-users, including, without limitation, claims, suits,
and liability for bodily or other injuries to end-users resulting from use of Licensee’s product not
caused solely by faults in Licensed Software as provided by LSI Logic to Licensee.
LSI Logic Corporation shall in no event be held liable for any loss, expenses, or damages of
Cont’d
Preface
vii
Preface,
Continued
Package Contents
Technical Support
Web Site
You should have received:
• a MegaRAID Express 500 PCI RAID Controller
• a CD with drivers, utilities, and documentation
• a MegaRAID Express 500 Hardware Guide (on CD)
• a MegaRAID Configuration Software Guide (on CD)
• a MegaRAID Operating System Drivers Guide (on CD)
• software license agreement (on CD)
• a warranty registration card (on CD)
If you need help installing, configuring, or running the MegaRAID Express 500 PCI
RAID Controller, call your LSI Logic OEM Technical Support representative at 678-728-
1250. Before you call, please complete the MegaRAID Problem Report form on the next
page.
We invite you to access the LSI Logic world wide web site at:
http://www.lsil.com.
MegaRAID Express500 Hardware Guide
viii
MegaRAID Problem Report Form
Customer Information MegaRAID Information
Name Today’s Date
Company Date of Purchase
Address Invoice Number
City/State Serial Number
Country
email address Cache Memory
Phone Firmware Version
Fax BIOS Version
System Information
Motherboard: BIOS manufacturer:
Operating System: BIOS Date:
Op. Sys. Ver.: Video Adapter:
MegaRAID
Driver Ver.:
Network Card: System Memory:
Other disk controllers
installed:
Description of problem:
Steps necessary to re-create problem:
1.
2.
3.
4.
CPU Type/Speed:
Other adapter cards
installed:
Logical Drive Configuration
Logical
Drive
RAID
Level
LD0
LD1
LD2
LD3
LD4
LD5
LD6
LD7
LD8
LD9
LD10
LD11
LD12
LD13
LD14
LD15
LD16
LD17
LD18
LD19
Stripe
Size
Logical Drive
Size
Cache
Policy
Read
Policy
Write
Policy
# of Physical
Drives
Preface
ix
Logical
Drive
LD20
LD21
LD22
LD23
LD24
LD25
LD26
LD27
LD28
LD29
LD30
LD31
LD32
LD33
LD34
LD35
LD36
LD37
LD38
LD39
RAID
Level
Stripe
Size
Logical Drive
Size
Cache
Policy
Read
Policy
Write
Policy
# of Physical
Drives
MegaRAID Express500 Hardware Guide
x
Physical Device Layout
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Channel 1
Preface
xi
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Target ID
Device Type
Logical Drive Number/ Drive Number
Manufacturer/Model Number
Firmware level
Channel 1
MegaRAID Express500 Hardware Guide
xii
Preface,
Continued
Disclaimer
This manual describes the operation of the LSI Logic MegaRAID Express 500 Disk Array
Controller. Although efforts have been made to assure the accuracy of the information contained
here, LSI Logic expressly disclaims liability for any error in this information, and for damages,
whether direct, indirect, special, exemplary, consequential or otherwise, that may result from such
error, including but not limited to the loss of profits resulting from the use or misuse of the manual
or information contained therein (even if LSI Logic has been advised of the possibility of such
damages). Any questions or comments regarding this document or its contents should be addressed
to LSI Logic at the address shown on the cover.
LSI Logic Corporation provides this publication “as is” without warranty of any kind, either
expressed or implied, including, but not limited to, the implied warranties of merchantability or
fitness for a specific purpose.
Some states do not allow disclaimer of express or implied warranties or the limitation or exclusion
of liability for indirect, special, exemplary, incidental or consequential damages in certain
transactions; therefore, this statement may not apply to you. Also, you may have other rights which
vary from jurisdiction to jurisdiction.
This publication could include technical inaccuracies or typographical errors. Changes are
periodically made to the information herein; these changes will be incorporated in new editions of
the publication. LSI Logic may make improvements and/or revisions in the product(s) and/or the
program(s) described in this publication at any time.
Requests for technical information about LSI Logic products should be made to your LSI Logic
authorized reseller or marketing representative.
Preface
xiii
FCC Regulatory Statement
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) this device may not
cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired
operation.
Warning
:
void the user's authority to operate the equipment.
Note:
the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation.
This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the
instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur
in a specific installation. If this equipment does cause harmful interference to radio or television reception, which can be determined
by turning the equipment off and on, try to correct the interference by one or more of the following measures:
1) Reorient or relocate the receiving antenna.
2) Increase the separation between the equipment and
3)
4) Consult the dealer or an experienced radio/TV technician
Shielded interface cables must be used with this product to ensure compliance with the Class B FCC
limits.
Changes or modifications to this unit not expressly approved by the party responsible for compliance could
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of
the receiver.
Connect the equipment into an outlet on a circuit different from
that to which the receiver is connected.
for help.
LSI Logic MegaRAID Express 500 PCI RAID Controller
Model Number:
FCC ID Number:
Series 475
IUESER475
Disclaimer
LSI Logic certifies only that this product will work correctly when this
product is used with the same jumper settings, the same system
configuration, the same memory module parts, and the same
peripherals that were tested by LSI Logic with this product. The
complete list of tested jumper settings, system configurations,
peripheral devices, and memory modules are documented in the LSI
Logic Compatibility Report for this product. Call your LSI Logic sales
representative for a copy of the Compatibility Report for this product.
MegaRAID Express500 Hardware Guide
xiv
1Overview
The MegaRAID® Express 500 PCI RAID controller is a high performance intelligent
PCI-to-SCSI host adapter with RAID control capabilities. The MegaRAID Express 500
provides reliability, high performance, and fault-tolerant disk subsystem management.
The MegaRAID Express 500 is part of the LSI Logic Intel i960RM/RS-based MegaRAID
controller family. The MegaRAID Express 500 is an entry level-to mid-range RAID
controller solution. MegaRAID Express 500 offers a cost-effective way to implement
RAID in a server.
The MegaRAID Express 500 has a 160M Ultra and Wide SCSI channel supporting data
transfer rates up to 160 megabytes per second (MB/s) per channel. The SCSI channel
supports up to fifteen non-Ultra SCSI devices. MegaRAID Express 500 includes
MegaRAID features and performance.
Features
SCSI Channel
MegaRAID Express 500:
provides a high performance I/O migration path while preserving existing PCI-SCSI software
•
performs SCSI data transfers up to 160 MB/s
•
performs synchronous operation on a wide LVD SCSI bus
•
allows up to 15 LVD SCSI devices on the wide bus
•
includes an Intel® i960RM that performs RAID calculations and routing
•
supports 8, 16, 32, 64, or 128 MB of SDRAM cache memory in a DIMM socket used for read
•
and write-back caching and RAID 5 parity generation
The MegaRAID Express 500 upgrade card includes one Ultra3 SCSI channel. The
channel is powered by a Q-Logic ISP10160A 160M SCSI processor.
NVRAM and Flash ROM
MegaRAID Express 500 firmware is stored in flash ROM for easy upgrade.
SCSI Connectors
MegaRAID Express 500 has one ultra high density 68-pin external connector for
external storage subsystem and one high density 68-pin internal connector.
A 32 KB x 8 NVRAM stores RAID system configuration information. The
Chapter 1 Overview
1
Single Ended and Differential SCSI Buses
The SCSI standard defines two electrical buses:
• a single ended bus
• low-voltage differential bus
Maximum Cable Length for SCSI Standards
Standard Single ended LVD Maximum Number of
SCSI I 6 m 12 m 7
Fast SCSI 6 m 12 m 7
Fast Wide SCSI 6 m 12 m 15
Ultra SCSI 1.5 m 12 m 7
Ultra SCSI 3 m 12 m 3
Wide Ultra SCSI 12 m 15
Wide Ultra SCSI 1.5 m 12 m 7
Wide Ultra SCSI 3 m 12 m 3
Ultra 2 SCSI 25 m 1
Ultra 2 SCSI 12 m 7
Wide Ultra 2 SCSI 25 m 1
Wide Ultra 2 SCSI 12 m 15
Ultra3 SCSI 25m 1
Ultra3 SCSI 12m 7
Wide Ultra3 SCSI 25m 1
Wide Ultra3 SCSI 12m 15
Drives
SCSI Bus Widths and Maximum Throughput
SCSI Standard SCSI Bus Width SCSI Throughput
SCSI I 8 bits 5 MB/s
Fast SCSI 8 bits 10 MB/s
Fast Wide SCSI 16 bits 20 MB/s
Ultra SCSI 8 bits 20 MB/s
Wide Ultra SCSI 16 bits 40 MB/s
Ultra 2 SCSI 8 bits 40 MB/s
Wide Ultra 2 SCSI 16 bits 80 MB/s
Ultra3 SCSI 8 bits 80 MB/s
Wide Ultra3 SCSI 16 bits 160 MB/s
MegaRAID Express 500 Hardware Guide
2
Documentation
The MegaRAID Express 500 technical documentation set includes:
• the MegaRAID Elite 1600 Hardware Guide
• the MegaRAID Configuration Software Guide
• the MegaRAID Operating System Drivers Guide
MegaRAID Configuration Hardware Guide This manual contains the RAID overview, RAID planning,
and RAID system configuration information you will need first. Read the MegaRAID
Express 500 Hardware Guide first.
MegaRAID Configuration Software Guide This manual describes the software configuration utilities that
configure and modify RAID systems.
MegaRAID Operating System Drivers Guide This manual provides detailed information about installing
the MegaRAID Express 500 operating system drivers.
Chapter 1 Overview
3
MegaRAID Express 500 Block Diagram
MegaRAID Express 500 Hardware Guide
4
2 Introduction to RAID
RAID (Redundant Array of Independent Disks) is an array of multiple independent hard
disk drives that provide high performance and fault tolerance. A RAID disk subsystem
improves I/O performance over a computer using only a single drive. The RAID array
appears to the host computer as a single storage unit or as multiple logical units. I/O is
expedited because several disks can be accessed simultaneously. RAID systems improve
data storage reliability and fault tolerance compared to single-drive computers. Data loss
because of a disk drive failure can be recovered by reconstructing missing data from the
remaining data and parity drives.
RAID Benefits
RAID has gained popularity because it improves I/O performance and increases storage
subsystem reliability. RAID provides data security through fault tolerance and redundant
data storage. The MegaRAID Express 500 management software configures and monitors
RAID disk arrays.
Improved I/O
Increased Reliability
Although disk drive capabilities have improved drastically, actual performance has been
improved only three to four times in the last decade. Computing performance has been
improved over 50 times during the same time period.
more power, and generate more noise and vibration than electronic devices. These factors
reduce the reliability of data stored on disks.
The electromechanical components of a disk subsystem operate more slowly, require
Chapter 2 Introduction to RAID
5
In This Chapter
The following topics are discussed:
Host-based RAID solution page 7
RAID overview page 8
Major Topic Subtopic turn to
Consistency check page 8
Fault tolerance page 8
Disk rebuild page 9
Hot spares Page 10
Hot swaps page 10
Parity page 11
Disk striping page 12
Disk mirroring page 13
Disk spanning page 14
Logical drive page 15
Logical drive states page 15
SCSI drive states page 15
Disk array types page 16
Enclosure management page 16
MegaRAID Express 500 Hardware Guide
6
MegaRAID Express 500 – Host-Based RAID Solution
RAID products are either:
• host-based or
• SCSI-to-SCSI
The MegaRAID Express 500 controller is a host-based RAID solution. MegaRAID
Express 500 is a PCI adapter card that is installed in any available PCI expansion slot in a
host system.
Host-Based
SCSI-to-SCSI
A host-based RAID product puts all of the RAID intelligence on an adapter card that is
installed in a network server. A host-based RAID product provides the best performance.
MegaRAID Express 500 is part of the file server, so it can transmit data directly across
the computer’s buses at data transfer speeds up to 132 MB/s.
The available sequential data transfer rate is determined by the following factors:
• the sustained data transfer rate on the motherboard PCI bus
• the sustained data transfer rate on the i960RM PCI to PCI bridge
• the sustained data transfer rate of the SCSI controller
• the sustained data transfer rate of the SCSI devices
• the number of SCSI channels
• the number of SCSI disk drives
Host-based solutions must provide operating system-specific drivers.
A SCSI-to-SCSI RAID product puts the RAID intelligence inside the RAID chassis and
uses a plain SCSI Host Adapter installed in the network server. The data transfer rate is
limited to the bandwidth of the SCSI channel. A SCSI-to-SCSI RAID product that has
two wide SCSI channels operating at speeds up to 160 MB/s must squeeze the data into a
single wide SCSI (160 MB/s) channel back to the host computer.
In SCSI-to-SCSI RAID products, the hard drive subsystem uses only a single SCSI ID,
which allows you to connect multiple drive subsystems to a single SCSI controller.
Chapter 2 Introduction to RAID
7
RAID Overview
RAID (Redundant Array of Independent Disks) is a collection of specifications that
describe a system for ensuring the reliability and stability of data stored on large disk
subsystems. A RAID system can be implemented in a number of different versions (or
RAID Levels). The standard RAID levels are 0, 1, 3, and 5. MegaRAID Express 500
supports all standard RAID levels and RAID levels 10, 30, and 50, special RAID versions
supported by MegaRAID Express 500.
Fault Tolerance
Fault tolerance is achieved through cooling fans, power supplies, and the ability to hot
swap drives. MegaRAID Express 500 provides hot swapping through the hot spare
feature. A hot spare drive is an unused online available drive that MegaRAID Express
500 instantly plugs into the system when an active drive fails.
After the hot spare is automatically moved into the RAID subsystem, the failed drive is
automatically rebuilt. The RAID disk array continues to handle request while the rebuild
occurs.
Consistency Check
In RAID, check consistency verifies the correctness of redundant data in an array. For
example, in a system with dedicated parity, checking consistency means computing the
parity of the data drives and comparing the results to the contents of the dedicated parity
drive.
MegaRAID Express 500 Hardware Guide
8
Disk Rebuild
You rebuild a disk drive by recreating the data that had been stored on the drive before
the drive failed.
Rebuilding can be done only in arrays with data redundancy such as RAID level 1, 3, 5,
10, 30, and 50.
Standby (warm spare) rebuild is employed in a mirrored (RAID 1) system. If a disk drive
fails, an identical drive is immediately available. The primary data source disk drive is the
original disk drive.
A hot spare can be used to rebuild disk drives in RAID 1, 3, 5, 10, 30, or 50 systems. If a
hot spare is not available, the failed disk drive must be replaced with a new disk drive so
that the data on the failed drive can be rebuilt.
The MegaRAID Express 500 controller automatically and transparently rebuilds failed
drives with user-definable rebuild rates. If a hot spare is available, the rebuild starts
automatically when a drive fails. MegaRAID Express 500 automatically restarts the
system and the rebuild if the system goes down during a rebuild.
Rebuild Rate
Physical Array
The rebuild rate is the fraction of the compute cycles dedicated to rebuilding failed drives.
A rebuild rate of 100 percent means the system is totally dedicated to rebuilding the failed
drive.
The MegaRAID Express 500 rebuild rate can be configured between 0% and 100%. At
0%, the rebuild is only done if the system is not doing anything else. At 100%, the rebuild
has a higher priority than any other system activity.
A RAID array is a collection of physical disk drives governed by the RAID management
software. A RAID array appears to the host computer as one or more logical drives.
Chapter 2 Introduction to RAID
9
Hot Spares
Hot Swap
A hot spare is an extra, unused disk drive that is part of the disk subsystem. It is usually in
standby mode, ready for service if a drive fails. Hot spares permit you to replace failed
drives without system shutdown or user intervention.
MegaRAID Express 500 implements automatic and transparent rebuilds using hot spare
drives, providing a high degree of fault tolerance and zero downtime. The MegaRAID
Express 500 RAID Management software allows you to specify physical drives as hot
spares. When a hot spare is needed, the MegaRAID Express 500 controller assigns the
hot spare that has a capacity closest to and at least as great as that of the failed drive to
take the place of the failed drive.
Important
Hot spares are employed only in arrays with redundancy, for
example, RAID levels 1, 3, 5, 10, 30, and 50.
A hot spare connected to a specific MegaRAID Express 500
controller can be used only to rebuild a drive that is
connected to the same controller.
A hot swap is the manual replacement of a defective physical disk unit while the computer
is still running. When a new drive has been installed, you must issue a command to
rebuild the drive.
MegaRAID Express 500 Hardware Guide
10
Parity
Parity generates a set of redundancy data from two or more parent data sets. The
redundancy data can be used to reconstruct one of the parent data sets. Parity data does
not fully duplicate the parent data sets. In RAID, this method is applied to entire drives or
stripes across all disk drives in an array. The types of parity are:
Type Description
Dedicated Parity The parity of the data on two or more disk drives is
stored on an additional disk.
Distributed
Parity
The parity data is distributed across all drives in the
system.
If a single disk drive fails, it can be rebuilt from the parity and the data on the remaining
drives.
RAID level 3 combines dedicated parity with disk striping. The parity disk in RAID 3 is
the last logical drive in a RAID set.
RAID level 5 combines distributed parity with disk striping. Parity provides redundancy
for one drive failure without duplicating the contents of entire disk drives, but parity
generation can slow the write process. A dedicated parity scheme during normal
read/write operations is shown below:
Chapter 2 Introduction to RAID
11
Disk Striping
Disk striping writes data across multiple disk drives instead of just one disk drive. Disk
striping involves partitioning each drive storage space into stripes that can vary in size
from 2 KB to 128 KB. These stripes are interleaved in a repeated sequential manner. The
combined storage space is composed of stripes from each drive. MegaRAID Express 500
supports stripe sizes of 2 KB, 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, or 128 KB.
For example, in a four-disk system using only disk striping (as in RAID level 0), segment
1 is written to disk 1, segment 2 is written to disk 2, and so on. Disk striping enhances
performance because multiple drives are accessed simultaneously; but disk striping does
not provide data redundancy.
Stripe Width
Stripe width is a measure of the number of disks involved in an array where striping is
implemented. For example, a four-disk array with disk striping has a stripe width of four.
Stripe Size
The stripe size is the length of the interleaved data segments that MegaRAID Express 500
writes across multiple drives. MegaRAID Express 500 supports stripe sizes of 2 KB, 4
KB, 8 KB, 16 KB, 32 KB, 64 KB, or 128 KB.
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Disk Mirroring
With mirroring (used in RAID 1), data written to one disk drive is simultaneously written
to another disk drive. If one disk drive fails, the contents of the other disk drive can be
used to run the system and reconstruct the failed drive. The primary advantage of disk
mirroring is that it provides 100% data redundancy. Since the contents of the disk drive
are completely written to a second drive, it does not matter if one of the drives fails. Both
drives contain the same data at all times. Either drive can act as the operational drive.
Disk mirroring provides 100% redundancy, but is expensive because each drive in the
system must be duplicated.
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Disk Spanning
Disk spanning allows multiple disk drives to function like one big drive. Spanning
overcomes lack of disk space and simplifies storage management by combining existing
resources or adding relatively inexpensive resources. For example, four 400 MB disk
drives can be combined to appear to the operating system as one single 1600 MB drive.
Spanning alone does not provide reliability or performance enhancements. Spanned
logical drives must have the same stripe size and must be contiguous. In the following
graphic, RAID 1 array is turned into a RAID 10 array.
This controller supports a span depth of eight. That means that eight RAID 1, 3 or 5
arrays can be spanned to create one logical drive.
Spanning for RAID 10, RAID 30, or RAID 50
Level Description
10 Configure RAID 10 by spanning two contiguous RAID 1 logical drives.
The RAID 1 logical drives must have the same stripe size.
30 Configure RAID 30 by spanning two contiguous RAID 3 logical drives.
The RAID 3 logical drives must have the same stripe size.
50 Configure RAID 50 by spanning two contiguous RAID 5 logical drives.
The RAID 5 logical drives must have the same stripe size.
Spanning two contiguous RAID 0 logical drives does not produce a new
Note:
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RAID level or add fault tolerance. It does increase the size of the logical
volume and improves performance by doubling the number of spindles.
Logical Drive
A logical drive is a partition in a physical array of disks that is made up of contiguous
data segments on the physical disks. A logical drive can consist of:
• an entire physical array
• more than one entire physical array
• a part of an array
•
parts of more than one array, or
•
a combination of any two of the above conditions
Logical Drive States
State Description
Optimal The drive operating condition is good. All configured drives are
Degraded The drive operating condition is not optimal. One of the configured
Failed The drive has failed.
Offline The drive is not available to MegaRAID Express 500.
SCSI Drive States
online
drives has failed or is offline.
A SCSI disk drive can be in one of these states:
State Description
Online
(ONLIN)
Ready
(READY)
Hot Spare
(HOTSP)
Fail
(FAIL)
Rebuild
(REB)
The drive is functioning normally and is a part of a configured
logical drive.
The drive is functioning normally but is not part of a configured
logical drive and is not designated as a hot spare.
The drive is powered up and ready for use as a spare in case an
online drive fails.
A fault has occurred in the drive placing it out of service.
The drive is being rebuilt with data from a failed drive.
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Disk Array Types
The RAID disk array types are listed in the following table:
Type Description
Software-
Based
SCSI to SCSI The array controller resides outside of the host computer and
Bus-Based The array controller resides on the bus (for example, a PCI or
The array is managed by software running in a host computer using
the host CPU bandwidth. The disadvantages associated with this
method are the load on the host CPU and the need for different
software for each operating system.
communicates with the host through a SCSI adapter in the host.
The array management software runs in the controller. It is
transparent to the host and independent of the host operating
system. The disadvantage is the limited data transfer rate of the
SCSI channel between the SCSI adapter and the array controller.
EISA bus) in the host computer and has its own CPU to generate
the parity and handle other RAID functions. A bus-based controller
can transfer data at the speed of the host bus (PCI, ISA, EISA, VLBus) but is limited to the bus it is designed for. MegaRAID
Express 500 resides on a PCI bus, which can handle data transfer
at up to 132 MB/s. With MegaRAID Express 500, the channel can
handle data transfer rates up to 160 MB/s per SCSI channel.
Enclosure Management
Enclosure management is the intelligent monitoring of the disk subsystem by software
and/or hardware.
The disk subsystem can be part of the host computer or separate from it. Enclosure
management helps you stay informed of events in the disk subsystem, such as a drive or
power supply failure. Enclosure management increases the fault tolerance of the disk
subsystem.
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