HP Surestore Disk Array FC60 HP SureStore E Disk Array FC60 Service Manual (A5 - Page 49
RAID 1, Volume Group
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Product Description Figure 18 RAID 0 Volume Group RAID 1 RAID 1 uses mirroring to achieve data redundancy. RAID 1 provides high availability and good performance, but at the cost of storage efficiency. Because all data is mirrored, a RAID 1 volume group has a storage efficiency of 50%. A RAID 1 volume group consists of exactly two disks configured as a mirrored pair. One disk is the data disk and the other is the disk mirror. The disks in a RAID 1 volume group are mirrored by the disk array hardware, which automatically writes data to both the data disk and the disk mirror. Once bound into a RAID 1 mirrored pair, the two disks cannot be accessed as 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 volume group 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 volume group operates in degraded mode. While in degraded mode the volume group is susceptible to the failure of the second disk. If both disks fail or become inaccessible simultaneously, the data on the volume group becomes inaccessible. Disk Array High Availability Features 49