HP A7143A RAID160 SA Controller Support Guide

RAID Technology Overview
Logical Drives and Arrays
Chapter 118
Disk failure, although rare, is potentially catastrophic. If a physical disk
fails, the logical drive it is assigned to will fail, and all of the data on that
logical drive will be lost.
To protect against data loss due to physical disk failure, logical drives
can be configured with fault tolerance. The RAID configurations that are
supported by the HP RAID160 SA controller are:
• RAID 0—Data Striping only (no fault tolerance)
• RAID 1—Data Mirroring only (fault tolerant)
• RAID 1+0—Drive Mirroring and Striping (fault tolerant)
• RAID 5—Distributed Data Guarding (fault tolerant)
• RAID ADG—Advanced Data Guarding (fault tolerant)
For any configuration except RAID 0, further protection against data loss
can be achieved by assigning a physical disk as an online spare (or hot
spare). Spare disk drives contain no data and must be in the same array
as the logical drive they are assigned to. Multiple spare disk drives can
be assigned to a logical drive, limited only by the availability of unused
physical disks in the array. When a spare disk drive is assigned to a
logical drive, it can only serve as a spare for the logical drive it is
assigned to. When a physical disk in the array fails, the controller
automatically rebuilds the information that was originally on the failed
disk, onto an online spare. The system is quickly restored to full
RAID-level data protection. In the unlikely event that another disk in
the array fails while data is being rewritten to the spare, the logical drive
may fail, depending on which RAID configuration is in use. See
Appendix A, Probability of Logical Drive Failure,for details.