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

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

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.

P5,6

Q7,8

P3,4

Q5,6 B5

P1,2

Q3,4 B4

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.

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