HP A7143A RAID160 SA Controller Support Guide, February 2007

Hard Drive Installation and Replacement

General Information About Hard Drive Failure

Appendix C

101

General Information About Hard Drive Failure

When a physical disk fails, the logical drive it belongs to will be affected. Each logical drive connected to a

RAID160 SA controller can be configured with be a different RAID level. For this reason, each logical drive

may be affected differently by a physical disk failure, depending on the fault-tolerance method (RAID level)

that has been configured on it.

• RAID 0 configurations cannot tolerate disk drive failure. If any physical disk in the array fails, the logical

drive will also fail.

• RAID 1 configurations, which are limited to two mirrored physical disks in an array, can tolerate one

physical disk failure.

• RAID 1+0 configurations can tolerate multiple physical disk failures as long as no failed disks are

mirrored to one another.

• RAID 5 configurations can tolerate one physical disk failure.

• RAID ADG configurations can tolerate simultaneous failure of two physical disks.

If more physical disks 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 will be rejected with unrecoverable

errors. The “Compromised Fault Tolerance” section discusses possible ways to recover from this situation.

Recognizing Disk Drive Failure

The LEDs on the front of each disk drive are visible through the front of the StorageWorks™ disk enclosures.

When a disk drive is configured as part of an array and attached to a powered-up controller, the status of the

drive can be determined from the illumination pattern of the LEDs.

Table E-1 describes the meaning of the various LED combinations.

Figure C-1 Figure E-1: Hard drive status LED indicators