Installation Guide - HP AD397A rx2660 SAS Smart Array P400 Controller

Fault Management
Fault Management in Supported RAID Configurations
Appendix B
31
Fault Management in Supported RAID Configurations
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 RAID 1 is configured with a single mirrored pair of disks. If one physical disk fails, the
remaining disk in the mirrored pair can still provide all the data.
RAID 1+0 A RAID 1+0 configuration has a minimum of four physical disks, and the total number of
physical disks is divisible by two to support mirrored pairs. In RAID 1+0, if a physical disk
fails, the remaining disk in any mirrored pair still provides all of the data that was on the
failed disk. 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 using a parity formula
and is typically written to an online spare physical disk. If a second physical disk fails
before the data from the initial physical disk failure has been rebuilt on the online spare
disk, the logical drive fails and data is lost.
ADG Similar to RAID 5, ADG 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 Smart Array Controllers see the HP
Smart Array P400 Support Guide, available at http://www.docs.hp.com in the “I/O Cards and Networking”
section.