Modular Smart Array (MSA1000) Reference Guide (September 2003)

Recovering from Hard Drive Failure
80 MSA1000 Reference Guide
Hard Drive Failure
When a hard drive fails, all logical drives that are in the same array will be
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 be failed.
■ RAID 1 and RAID 1+0 configurations can tolerate multiple drive failures, as
long as none of the failed drives are mirrored to one another.
■ RAID 5 configurations can tolerate one drive failure.
■ RAID ADG configurations can tolerate simultaneous failure of two drives in
the array.
■ Spare hard drive configuration guidelines include:
— A spare must be assigned to each individual array separately.
— A spare must be greater than or equal to any drive that it is intended to
replace.
— The same spare can be assigned to multiple Controllers as long as its
capacity is greater than or equal to any drives in that array.
Note: Only remove hard drives that have been failed or marked as degraded by the
controller.
If more hard drives are failed than the fault-tolerance method allows, fault
tolerance is “compromised” and the logical drive is failed. In this case, all requests
from the operating system will be rejected with “unrecoverable” errors. The
section on Compromised Fault Tolerance later in this chapter discusses possible
ways to recover from this situation.