Effects of a hard drive failure, Compromised fault tolerance, Recovering from compromised fault tolerance – HP 60-Modular-Smart-Array User Manual
Page 30: Factors to consider before replacing hard drives
Troubleshooting 30
For additional information about diagnosing hard drive problems, see the HP ProLiant Servers
Troubleshooting Guide.
CAUTION: Sometimes, a drive that has previously failed may seem to be operational after the system is
power-cycled or (for a hot-pluggable drive) after the drive has been removed and reinserted. However,
continued use of such marginal drives may eventually result in data loss. Replace the marginal drive as soon
as possible.
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 may 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 (with no spares assigned).
•
RAID 5 configurations can tolerate one drive failure (with no spares assigned).
•
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 storage enclosure ("
3.
Power up the storage enclosure ("
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: