HP A7143A RAID160 SA Controller Support Guide

Hard Drive Installation and Replacement
General Information About Hard Drive Failure
Appendix C 141
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.