HP Surestore Disk Array 12h - And FC60, Advanced User'S Manual, Page: 53 / 466

Disk Array High Availability Features
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pair. For highest data availability, each disk in the mirrored pair must be located in a
different enclosure.
When a disk fails, the disk array automatically uses the remaining disk of the mirrored pair
for data access. A RAID 0/1 LUN can survive the failure of multiple disks, as long as one
disk in each mirrored pair remains accessible. Until the failed disk is replaced (or a rebuild
on a global hot spare is completed), the LUN operates in degraded mode. While in degraded
mode, the LUN is susceptible to the failure of the second disk of the pair. If both disks fail
or become inaccessible simultaneously, the data on the LUN becomes inaccessible.
Figure 20 illustrates the distribution of data in a four-module RAID 0/1 LUN. The disk block
addresses in the stripe proceed sequentially from the first pair of mirrored disks (disks 1
and 2) to the second pair of mirrored disks (disks 3 and 4), then again from the first
mirrored disks, and so on.
Figure 20
RAID 0/1
LUN
RAID 3
RAID 3 uses parity to achieve data redundancy and disk striping to enhance performance.
Data is distributed across all but one of the disks in the RAID 3 LUN. The remaining disk is
used to store parity information for each data stripe. A RAID 3 LUN consists of three or