Troubleshooting 30
•
RAID 6 with ADG configurations can tolerate simultaneous failure of two drives (with no spares
assigned).
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.
Check for loose, dirty, broken, or bent cabling and connectors on all devices.
2.
Power down the MDS600 ("
Power down
" on page
13
).
3.
Power up the MDS600.
In some cases, a marginal drive is operational long enough to allow backup of important files.
4.
Make copies of important data, if possible.
5.
Replace any failed drives.
Factors to consider before replacing hard drives
You can replace hard drives without powering down the system. However, 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, refer to 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 when removing failed drives, take the following
precautions:
•
Do not remove a degraded drive if any other drive in the array is offline (the online LED is off). In this
situation, removing any other drive in the array causes data loss.
Exceptions: