Compaq 166207-B21 - Smart Array 5302/32 RAID... User manual

COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
Compaq Advanced Data Guarding
Option Software
Reference Guide
Part Number 283954-001
May 2002 (First Edition)

COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
© 2002 Compaq Information Technologies Group, L.P.
Compaq and the Compaq logo are trademarks of Compaq Information Technologies Group,
L.P. in the U.S. and/or other countries. Microsoft, Windows, and Windows NT are trademarks
of Microsoft Corporation in the U.S. and/or other countries.
All other product names mentioned herein may be trademarks of their respective companies.
Compaq shall not be liable for technical or editorial errors or omissions contained herein. The
information in this document is provided “as is” without warranty of any kind and is subject to
change without notice. The warranties for Compaq products are set forth in the express limited
warranty statements accompanying such products. Nothing herein should be construed as
constituting an additional warranty.
Compaq Advanced Data Guarding Option Software Reference Guide
May 2002 (First Edition)
Part Number 283954-001

Compaq Advanced Data Guarding Option Software Reference Guide iii
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
Contents
About This Guide
Symbols in Text...................................................................................................................v
Text Conventions .............................................................................................................. vi
Getting Help ...................................................................................................................... vi
Compaq Technical Support......................................................................................... vi
Compaq Website........................................................................................................ vii
Compaq Authorized Reseller..................................................................................... vii
Reader’s Comments ......................................................................................................... vii
Chapter 1
Overview of RAID ADG
Comparing RAID ADG to Other RAID Methods........................................................... 1-2
Probability of Logical Drive Failure......................................................................... 1-3
Choosing a RAID Method............................................................................................... 1-5
Chapter 2
System Setup
Enabling RAID ADG ...................................................................................................... 2-1
Configuring the System with RAID ADG ...................................................................... 2-3
Configuring a New System....................................................................................... 2-3
Migrating an Existing Logical Drive to RAID ADG................................................ 2-5
Migrating a RAID ADG Volume to Another Controller.......................................... 2-7
Assigning Online Spares after System Configuration..................................................... 2-7
Performance Tuning ........................................................................................................ 2-8
Changing the Cache Read/Write Ratio ..................................................................... 2-9
Optimizing the Stripe Size ........................................................................................ 2-9

Contents
iv Compaq Advanced Data Guarding Option Software Reference Guide
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM

Compaq Advanced Data Guarding Option Software Reference Guide v
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
About This Guide
This guide provides step-by-step instructions for installation, and reference
information for operation, troubleshooting, and future upgrades for the Compaq
Advanced Data Guarding Option Software.
Symbols in Text
These symbols may be found in the text of this guide. They have the following
meanings.
WARNING: Text set off in this manner indicates that failure to follow directions
in the warning could result in bodily harm or loss of life.
CAUTION: Text set off in this manner indicates that failure to follow directions could
result in damage to equipment or loss of information.
IMPORTANT: Text set off in this manner presents clarifying information or specific
instructions.
NOTE: Text set off in this manner presents commentary, sidelights, or interesting points of
information.

About This Guide
vi Compaq Advanced Data Guarding Option Software Reference Guide
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
Text Conventions
This document uses the following conventions:
• Italic type is used for complete titles of published guides or variables. Variables
include information that varies in system output, in command lines, and in
command parameters in text.
• Bold type is used for emphasis, for onscreen interface components (window
titles, menu names and selections, button and icon names, and so on), and for
keyboard keys.
• Monospace typeface is used for command lines, code examples, screen
displays, error messages, and user input.
• Sans serif typeface is used for uniform resource locators (URLs).
Getting Help
If you have a problem and have exhausted the information in this guide, you can get
further information and other help in the following locations.
Compaq Technical Support
In North America, call the Compaq Technical Support Phone Center at
1-800-OK-COMPAQ. This service is available 24 hours a day, 7 days a week. For
continuous quality improvement, calls may be recorded or monitored. Outside North
America, call the nearest Compaq Technical Support Phone Center. For telephone
numbers of worldwide Technical Support Centers, go to www.compaq.com.
Be sure to have the following information available before you call Compaq:
• Technical support registration number (if applicable)
• Product serial number
• Product model name and number
• Applicable error messages
• Add-on boards or hardware

About This Guide
Compaq Advanced Data Guarding Option Software Reference Guide vii
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: a-frnt
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:40 PM
• Third-party hardware or software
• Operating system type and revision level
Compaq Website
For information on this product, as well as the latest drivers and flash ROM images,
go to www.compaq.com.
Compaq Authorized Reseller
For the name of your nearest Compaq authorized reseller:
• In the United States, call 1-800-345-1518.
• In Canada, call 1-800-263-5868.
• Elsewhere, see the Compaq website for locations and telephone numbers.
Reader’s Comments
Compaq welcomes your comments on this guide. Please send your comments and
suggestions by email to [email protected].

Compaq Advanced Data Guarding Option Software Reference Guide 1-1
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: b-ch1 overview of RAID ADG
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:41 PM
1
Overview of RAID ADG
Advanced Data Guarding (RAID ADG) is a fault-tolerance method that uses two
different and independent sets of parity data. A logical volume using this
exceptionally high level of data protection can tolerate the simultaneous failure of
two hard drives without suffering downtime or data loss.
B1
B3
P5,6
Q7,8
B2
B7
P3,4
Q5,6 B5
B8
P1,2
Q3,4 B4
B6
P7,8
Q1,2
Figure 1-1: Array using RAID ADG, showing data blocks
(B) and two parity data sets (P, Q)
RAID ADG also makes efficient use of drive space, since the two sets of parity data
occupy a total drive space equivalent to two hard drives. The amount of drive space
used for parity data is independent of the total number of hard drives in the logical
volume.

Overview of RAID ADG
1-2 Compaq Advanced Data Guarding Option Software Reference Guide
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: b-ch1 overview of RAID ADG
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:41 PM
Theoretically, RAID ADG can support a logical volume that spans over 200 hard
drives without any great risk of data loss. However, currently existing array
controllers and storage systems support no more than 14 drives per channel. Thus, the
largest obtainable logical volume, using a 4-channel controller, spans 56 hard drives.
Comparing RAID ADG to Other RAID Methods
Table 1-1 summarizes the most important features of the different RAID methods
that are supported by Compaq array controllers. For more detailed information, refer
to the user guide for the Smart Array controller that is installed in the system.
Table 1-1: Comparison of RAID Methods
RAID 0 RAID 1+0 RAID 5 RAID ADG
Alternative name Striping (no
fault tolerance)
Mirroring Distributed
Data Guarding
Advanced Data
Guarding
Usable drive space* 100% 50% 67% to 93% 50% to 96%
Usable drive space
formula
n n/2 (n-1)/n(n-2)/n
Minimum number of
physical drives
1 2 3 4
Tolerates failure of
one physical drive?
No Yes Yes Yes
Tolerates
simultaneous failure
of more than one
physical drive?
No Only if no two
failed drives are
in a mirrored pair
No Yes
Read performance High High High High
Write performance High Medium Low Low
Relative cost Low High Medium Medium
*Values for usable drive space are calculated with these assumptions: (1) All physical drives in the
array have the same capacity; (2) Online spares are not used; (3) No more than 14 physical drives
are used per array for RAID 5; (4) No more than 56 drives are used with RAID ADG.

Overview of RAID ADG
Compaq Advanced Data Guarding Option Software Reference Guide 1-3
COMPAQ CONFIDENTIAL
Writer: John Turner File Name: b-ch1 overview of RAID ADG
Codename: adg2 Part Number: 283954-001 Last Saved On: 5/22/02 12:41 PM
Probability of Logical Drive Failure
The probability that a logical drive will fail depends on the RAID level setting.
• A RAID 0 logical drive will fail if only one physical drive fails.
• For a RAID 1+0 logical drive, the failure situation is complex.
— The maximum number of physical drives that can fail without causing
failure of the logical drive is n/2, where nis the number of hard drives in the
array. This maximum is reached only if no failed drive is mirrored to any
other failed drive. In practice, a logical drive usually fails before this
maximum is reached. As the number of failed physical drives increases, it
becomes increasingly unlikely that a newly failed drive is not mirrored to a
previously failed drive.
— The failure of only two physical drives is enough to cause a logical drive to
fail if the two drives happen to be mirrored to each other. The risk of such
mutually mirrored drives failing decreases as the number of mirrored pairs in
the array increases.
• A RAID 5 logical drive (with no online spare) fails if two physical drives fail.
• A RAID ADG logical drive (with no online spare) fails when three physical
drives fail.
At any given RAID level, the probability of logical drive failure increases as the
number of physical drives in the logical drive increases.
The graph in Figure 1-2 provides more quantitative information. The data for this
graph is calculated from the mean time between failure (MTBF) value for a typical
physical drive, assuming that no online spares are present. If an online spare is added
to any of the fault-tolerant RAID configurations, the probability of logical drive
failure is further decreased.