Compaq 179740-001 - ProLiant - 3000 Quick reference guide

White Paper
November 1999
11DT-119A-WWEN
Prepared by Storage Products
Division
Compaq Computer Corporation
Contents
Rapid Recovery with Hot-
Plug Drives.................................3
Guidelines when hot-
plugging a drive ........................3
Guidelines when Insight
Manager indicates that a
drive is degraded and should
be replaced...............................4
Conclusion .................................6
Hot-Plug Disk Drive Removal
and Replacement Guidelines for
Compaq Smart Array
Controllers
Abstract: The purpose of this paper is to communicate to customers
the guidelines for implementing hot-plug removal and replacement
of hard drives when using Compaq Smart Array Controllers.
Compaq is fully committed to providing the ideal client/server high
availability solution for customers. High availability features in
Compaq Smart Array Controllers include hot-pluggable hard drives.
With hot-pluggable hard drives, customers can remove and replace
one or several drives within a server while the system is online for
rapid recovery while minimizing interruption of the network.
In order to maximize high availability, Compaq has issued customer
guidelines on extending and implementing the removal and
replacement of hot-pluggable hard drives.

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Notice
The information in this publication is subject to change without notice and is provided “AS IS” WITHOUT
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INFORMATION REMAINS WITH RECIPIENT. IN NO EVENT SHALL COMPAQ BE LIABLE FOR
ANY DIRECT, CONSEQUENTIAL, INCIDENTAL, SPECIAL, PUNITIVE OR OTHER DAMAGES
WHATSOEVER (INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS
PROFITS, BUSINESS INTERRUPTION OR LOSS OF BUSINESS INFORMATION), EVEN IF
COMPAQ HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
The limited warranties for Compaq products are exclusively set forth in the documentation accompanying
such products. Nothing herein should be construed as constituting a further or additional warranty.
This publication does not constitute an endorsement of the product or products that were tested. The
configuration or configurations tested or described may or may not be the only available solution. This test
is not a determination or product quality or correctness, nor does it ensure compliance with any federal
state or local requirements.
Product names mentioned herein may be trademarks and/or registered trademarks of their respective
companies.
Compaq, Contura, Deskpro, Fastart, Compaq Insight Manager, LTE, PageMarq, Systempro, Systempro/LT,
ProLiant, TwinTray, ROMPaq, LicensePaq, QVision, SLT, ProLinea, SmartStart, NetFlex, DirectPlus,
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CompaqCare (design), Aero, SmartStation, MiniStation, and PaqRap, registered United States Patent and
Trademark Office.
Netelligent, Armada, Cruiser, Concerto, QuickChoice, ProSignia, Systempro/XL, Net1, LTE Elite,
Vocalyst, PageMate, SoftPaq, FirstPaq, SolutionPaq, EasyPoint, EZ Help, MaxLight, MultiLock,
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Pentium is a registered trademark of Intel Corporation.
Copyright ©1999 Compaq Computer Corporation. All rights reserved. Printed in the U.S.A.
Hot-Plug Disk Drive Removal and Replacement Guidelines for Compaq Smart Array Controllers
White Paper prepared by Storage Products Division
First Edition (November 1999)
Document Number 11DT-119A-WWEN

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11DT-119A-WWEN
Rapid Recovery with Hot-Plug Drives1
Compaq is the clear leader in high availability rapid recovery solutions. With Compaq Pre-
Failure Warranty, system administrators can proactively schedule downtime for maintenance and
not interrupt critical business operations that rely on these enterprise servers. In addition, with
hot-pluggable drives attached to Compaq Smart Array controllers, customers can remove and
replace one or several drives within a server while the system is online, which minimizes the
interruption of the network. To ensure maximum availability, however, Compaq recommends
that customers follow the guidelines listed below in removing and replacing hot-plug drives in
Smart Array controllers:
For customers who are utilizing Compaq Smart Array Controllers:2
Note: User intervention is required if customers are not utilizing an intelligent array controller
Definitions:
Drive Array – A drive array is a physical grouping of up to 56 physical drives (members) per
array.
Logical drive – A logical drive is all of or a portion of an array with RAID 0, 1 (and derivative
0+1), 4, and 5 striping all drives of an array.
Fault tolerant RAID – All logical drives in an array must be configured with some sort of fault
tolerant RAID (1, 0+1, 4, or 5). Hot-plugging a member of an array with any logical drive
configured for RAID 0 will result in the loss of data on that logical drive.
Hot-Plugging –Hot-Plugging a disk drive is defined as physically removing a disk drive from the
storage enclosure while powered up and online.
Guidelines when hot-plugging a drive
Customers should be able to hot-plug a drive during normal activity. It should be understood,
however, that hot-plugging a disk drive will affect system performance and fault tolerance.
IMPORTANT: It is therefore recommended that disk drive replacement be performed during low activity
periods whenever possible. In addition, a current valid backup should be available of the logical drives in
the array of the drive being replaced, even if drive replacement is being made during server downtime.
When a disk drive is hot-plugged, although the system is functionally operational, the disk
subsystem may no longer be fault tolerant. Fault tolerance will be lost until the removed drive is
subsequently replaced and the rebuild operation is completed. (This will take several hours even
if the system is not busy while the rebuild is in progress). If another drive in the array should
incur an error during the period when fault tolerance is unavailable, it is possible to cause a fatal
system error due to a data error. If another drive fails during this period, the entire contents of the
array will be lost.
1Certain restrictions and exclusions apply. Requires that servers use Compaq Insight Manager in order to implement Pre-Failure
alerting.
2CAUTION: Not following these recommended guidelines can result in data loss.

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Note: Therefore, Compaq recommends that disk drive replacement should be performed during low
activity periods whenever possible. In addition, a current valid backup should be available of the logical
drives in the array of the drive being replaced, even if drive replacement is being made during server
downtime.
Guidelines when Insight Manager indicates that a drive
is degraded and should be replaced
EXAMPLE: Using one hot-plug replacement example, a system administrator for a large
business uses Compaq Smart Array Controllers on his servers. Compaq Insight Manager has
indicated that a drive is degraded and should be replaced under the Pre-Failure Warranty. The
system administrator should follow the guidelines outlined below for maximum availability on
his server:
•All physical drives in the affected array should be present and have the online LED Indicators
illuminated before removing the degraded hot-plug drive. If any online LED Indicators are
flashing (indicating a rebuild) or not illuminated, the degraded drive should not be hot-
plugged.
For step-by-step instructions on hot-plugging your hard drive, refer to the ProLiant Setup and
Installation Guide.
•If fault-tolerance is currently being used to recover from errors from other drives in the array
(such as media errors or signal-integrity errors), loss of fault-tolerance following a drive
removal may result in unrecoverable errors being reported to the host operating system or
failure of the entire array. To verify that such errors are not presently occurring, and before
removing the degraded drive, consider using Insight Manager to examine the error counters
recorded for each physical drive in the array.
•The customer must follow Compaq cabling guidelines when configuring an array to
implement the best possible cabling solution for his server.
•The customer should check for cabling configurations that are not supported. Signal integrity
errors may be injected into the SCSI bus when an active drive is hot-plugged.
•The customer should make sure fault tolerance is not currently being used to recover from
errors to other drives in the array, such as media errors or signal integrity errors. Loss of fault
tolerance following a drive replacement may result in problems.
•If the customer is upgrading to larger drives in the array, follow the previously stated rules
and ensure that each drive has completed its rebuild before adding the next new drive to the
array.

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Table 1 shows hot-plug hard drive LED indicator status combinations.
Table 1
Hot-Plug Hard Drive LED Indicator Status Combinations
1
Activity 2 Online 3Fault Means
On Off Off Do not remove the drive. Removing a
drive during this process will cause data
loss.
The drive is being accessed and is not
configured as part of an array.
On Flashing Off Do not remove the drive. Removing a
drive during this process will cause data
loss.
The drive is rebuilding or undergoing capacity
expansion.
Flashing Flashing Flashing Do not remove the drive. Removing a
drive during this process will cause data
loss.
The drive is part of an array being selected
by the Array Configuration Utility.
-Or-
The Options ROMPaq is upgrading the drive.
Off Off Off OK to replace the drive online if a predictive
failure alert is received (see the following
section for details) and the drive is attached
to an array controller.
The drive is not configured as part of an
array.
-Or-
If this drive is part of an array, then a
powered-on controller is not accessing the
drive.
-Or-
The drive is configured as an online spare.
CAUTION: In extreme cases, when the number of errors is greater than the firmware error recovery is able
to sustain, hot-plugging on an online drive may cause some unrecoverable errors to be reported to the
operating system or may cause a complete failure of the array. Refer to your operating system
documentation for more information on implications, as well as possible recovery options.
IMPORTANT: Before replacing a degraded drive, use Compaq Insight Manager to examine the error
counters recorded for each physical drive in the array to verify that such errors are not presently occurring.

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The system administrator should also be aware of the following Compaq guidelines cautioning
unsafe hot-plug replacement:
•Do not remove a degraded drive if any other member of the array is off-line (the online LED
indicator is off). No other drive in the array can be hot-plugged without data loss with the
possible exception of utilizing RAID 0+1 as a fault tolerant form.
Refer to your Smart Array Controller’s user guide for information on fault tolerance options.
•Do not remove a degraded drive if any member of an array is missing (previously removed
and not yet replaced).
•Do not remove a degraded drive if any member of an array is being rebuilt unless the drive
being rebuilt has been configured as an online spare. The drive’s
online LED indicators will be flashing, indicating that a replaced drive is being rebuilt from
data stored on the other drives.
Note: An online spare will not activate and start rebuilding after a predictive failure alert, as the degraded
drive is still online. The online spare only activates after a drive in the array has failed.
•Do not replace multiple degraded drives at the same time (for example, when the system is
off), since the fault-tolerance may be compromised. When a drive is replaced, the controller
uses data from the other drives in the array to reconstruct data on the replacement drive. If
more than one drive is removed, a complete data set is not available to reconstruct data on the
replacement drive(s) and permanent data loss could occur.
CAUTION: Do not turn off an attached disk enclosure when the server containing the Smart Array
Controller is powered on. Also, do not turn on the server before turning on the disk enclosure. If these
ordering rules are not followed, the Smart Array Controller may mark these external drives as “failed,” which
could result in permanent data loss.
Conclusion
Compaq provides superior rapid recovery features in its Compaq Smart Array Controllers that
include hot-pluggable hard drives for high availability. In order to achieve maximum availability,
however, customers should follow the recommended Compaq guidelines for removal and
replacement.