HP Smart Array (RAID) Host Bus Adapters manual Effects of a hard drive failure

Page 28

Effects of a hard drive failure

When a hard drive fails, all logical drives that are in the same array are affected. Each logical drive in an array might be using a different fault-tolerance method, so each logical drive can be affected differently.

•RAID 0 configurations cannot tolerate drive failure. If any physical drive in the array fails, all non- fault-tolerant (RAID 0) logical drives in the same array will also fail.

•RAID 1+0 configurations can tolerate multiple drive failures as long as no failed drives are mirrored to one another.

•RAID 5 configurations can tolerate one drive failure.

•RAID 6 (ADG) configurations can tolerate the simultaneous failure of two drives.

Compromised fault tolerance

If more hard drives fail than the fault-tolerance method allows, fault tolerance is compromised, and the logical drive fails. In this case, all requests from the operating system are rejected with unrecoverable errors. You are likely to lose data, although it can sometimes be recovered (refer to "Recovering from compromised fault tolerance" on page 28).

One example of a situation in which compromised fault tolerance may occur is when a drive in an array fails while another drive in the array is being rebuilt. If the array has no online spare, any logical drives in this array that are configured with RAID 5 fault tolerance will fail.

Compromised fault tolerance can also be caused by non-drive problems, such as a faulty cable or temporary power loss to a storage system. In such cases, you do not need to replace the physical drives. However, you may still have lost data, especially if the system was busy at the time that the problem occurred.

Recovering from compromised fault tolerance

If fault tolerance is compromised, inserting replacement drives does not improve the condition of the logical volume. Instead, if the screen displays unrecoverable error messages, perform the following procedure to recover data:

1.Power down the entire system, and then power it back up. In some cases, a marginal drive will work again for long enough to enable you to make copies of important files.

If a 1779 POST message is displayed, press the F2 key to re-enable the logical volumes. Remember that data loss has probably occurred and any data on the logical volume is suspect.

2.Make copies of important data, if possible.

3.Replace any failed drives.

4.After you have replaced the failed drives, fault tolerance may again be compromised. If so, cycle the power again. If the 1779 POST message is displayed:

a.Press the F2 key to re-enable the logical drives.

b.Recreate the partitions.

c.Restore all data from backup.

To minimize the risk of data loss that is caused by compromised fault tolerance, make frequent backups of all logical volumes.

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Contents October 2006 Second Edition Part Number Audience assumptions Contents Electrostatic discharge Hardware features Controller specificationsMain components on the board This sectionPage Overview of the installation procedure Quick installation procedure Windows or LinuxOverview of the installation procedure Before beginning the installation Preparing the server Installing the controller hardwareInstalling the controller board Connecting internal storage Connecting storage devicesConnecting external storage SAS cable part numbers To order additional cables, use the option kit part numberUpdating the firmware Methods for updating the firmware Windows or LinuxUtilities available for configuring an array Configuring an arrayComparing the utilities Using Orca Select Create Logical DriveUsing ACU Systems using Microsoft Windows Installing device drivers and Management AgentsSystems using Linux A system that already has Linux installed Replacing or adding a battery Upgrading or replacing controller optionsUpgrading or replacing controller options Upgrading or replacing controller options Upgrading or replacing controller options Replacing the cache module or controller Upgrading or replacing controller options Upgrading or replacing controller options Upgrading or replacing controller options Replacing, moving, or adding hard drives Identifying the status of a hard driveRecognizing hard drive failure Terminate the current operation and cause data lossRecovering from compromised fault tolerance Compromised fault toleranceEffects of a hard drive failure Replacing hard drives Automatic data recovery rebuildFactors to consider before replacing hard drives Case 1 An uncorrectable read error has occurred Time required for a rebuildUpgrading hard drive capacity Case 2 The replacement drive has failedCase 3 Another drive in the array has failed Moving drives and arrays Adding drivesReplacing, moving, or adding hard drives Diagnosing array problems Controller board runtime LEDsBattery pack LEDs Diagnostic tools Post messagesPreventing electrostatic discharge Electrostatic dischargeGrounding methods to prevent electrostatic discharge Regulatory compliance notices Federal Communications Commission noticeModifications CablesEuropean Union regulatory notice Bsmi notice Japanese class a noticeKorean class a notice Battery replacement notice Taiwan battery recycling noticeAcronyms and abbreviations Smart Array Index Post error messages
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