HP Surestore Disk Array 12h and FC60 - Manual (Page 52)

52 Disk Array High Availability Features
individual disks. For highest data availability, each disk in the mirrored pair must be
located in a different enclosure.
When a data disk or disk mirror in a RAID 1 LUN fails, the disk array automatically uses the
remaining disk for data access. 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. If both disks fail or become inaccessible
simultaneously, the data on the LUN becomes inaccessible.
Figure 19 shows the distribution of data on a RAID 1 LUN. Note that all data on the data
disk is replicated on the disk mirror.
Figure 19 RAID 1 LUN
RAID 0/1
RAID 0/1 uses mirroring to achieve data redundancy and disk striping to enhance
performance. It combines the speed advantage of block striping with the redundancy
advantage of mirroring. Because all data is mirrored, a RAID 0/1 LUN has a storage
efficiency of 50%.
A RAID 0/1 LUN contains an even number of from four to 30 disks. One half of the disks are
primary disks and the other half are disk mirrors. The disks in a RAID 0/1 LUN are mirrored
by the disk array hardware, which automatically writes data to both disks in the mirrored