Compromised Fault Tolerance; Recovering From Compromised Fault Tolerance; Factors To Consider Before Replacing Hard Drives - HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual

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.
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. Perform the following procedure to recover data:
1. Power down the enclosure (see
2. Check for loose, dirty, broken, or bent cabling and connectors on all devices.
3. Power up the enclosure (see
NOTE:
In some cases, a marginal drive is operational long enough to allow backups of important
files.
4. Make copies of important data, if possible.
5. Replace any failed drives. Read
the failed hard drives.

Factors to consider before replacing hard drives

In systems that use external data storage, be sure that the server is the first unit to be powered down and
the last to be powered back up. Taking this precaution ensures that the system does not erroneously mark
the drives as failed when the server is powered up.
Before replacing a degraded drive:
• Open HP SIM and inspect the Error Counter window for each physical drive in the same array
to confirm that no other drives have any errors. For details, see the HP SIM documentation
on the Management CD.
• Be sure that the array has a current, valid backup.
• Use replacement drives that have a capacity at least as great as that of the smallest drive in the
array. The controller immediately fails drives that have insufficient capacity.
To minimize the likelihood of fatal system errors, take these precautions when removing failed drives:
• Do not remove a degraded drive if any other drive in the array is offline (the online LED is off). In
this situation, no other drive in the array can be removed without data loss.
Exceptions:
• When RAID 1+0 is used, drives are mirrored in pairs. Several drives can be in a failed
condition simultaneously (and they can all be replaced simultaneously) without data loss, as
long as no two failed drives belong to the same mirrored pair.
• When RAID 6 with ADG is used, two drives can fail simultaneously (and be replaced
simultaneously) without data loss.
Powering down).
Powering up).
Factors to consider before replacing hard drives before replacing
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