HP A7143A RAID160 SA Controller Support Guide

RAID160 SA Controller Overview
Board Components and Features
Chapter 234
If a physical disk fails in RAID 1, RAID 1+0, RAID 5, or ADG, the
system will still process I/O requests, but at a reduced performance
level. Replace the failed physical disk as soon as possible to restore
performance and full fault tolerance for the logical drive it belongs to.
The risk of continuing operations without replacing a failed physical
disk varies depending on the RAID level that has been configured:
— RAID 1: If RAID 1 is configured, the result will be a single
mirrored pair of disks. If one physical disk fails, the remaining
disk in the mirrored pair can still provide all of the data.
— RAID 1+0: A RAID 1+0 configuration will have a minimum of 4
physical disks, and the total number of physical disks will be
divisible by 2 (to support mirrored pairs). In RAID 1+0, if a
physical disk fails, the remaining disk in any mirrored pair will
still provide all of the data that was on the failed disk. In fact,
several physical disks in an array can fail without incurring data
loss, as long as no two failed physical disks belong to the same
mirrored pair.
— RAID 5: If a physical disk fails in a RAID 5 configuration, data
is recovered via a parity formula and is typically written to an
on-line spare physical disk. If a second physical disk fails before
the data from the initial physical disk failure has been rebuilt on
the on-line spare disk, the logical drive will fail and data will be
lost.
— ADG: Similar to RAID 5, ADG also relies on a parity scheme to
rebuild data if a physical disk fails. However, in an ADG
configuration the parity data is duplicated on two different
physical disks. As a result, ADG can support the failure of two
physical disks without data loss.
For a more detailed description of the RAID levels supported by the
HP A7143A RAID160 SA controller see Chapter 1, “RAID
Technology Overview,” on page 11.
For detailed information on the probability of logical drive failure,
see Appendix A, “Probability of Logical Drive Failure,” on page 133.
• Recovery ROM is a redundancy feature that ensures continuous
system availability by providing a backup ROM. This feature
protects against corruption of a ROM image (caused, for example, by
power fluctuation during ROM upgrade). If corruption occurs, the
server automatically restarts using the remaining good copy of the