Written by Debi Riedel, Director of Technology Resources, Datatrend Technologies, Inc.
A Redundant Array of Independent Disks (RAID) is a method of configuring drives for high availability and high performance.
RAID is an ordered collection, or group, of physical devices (disk drive modules) that are used to define logical volumes or devices. An array is a type of MDisk that is made up of disk drives. These drives are members of the array. Each array has a RAID level. RAID levels provide different degrees of redundancy and performance, and they have different restrictions on the number of members in the array.
IBM Storwize® V7000 supports hot-spare drives. When a RAID member drive fails, the system automatically replaces the failed member with a hot-spare drive and resynchronizes the array to restore its redundancy.
Figure 1 shows the relationships of the RAID components on the system.
Supported RAID levels are RAID 0, RAID 1, RAID 5, RAID 6, or RAID 10.
RAID 0 arrays have no redundancy and do not support hot-spare takeover.
RAID 1 provides disk mirroring, which duplicates data between two drives. A RAID 1 array is internally identical to a two-member RAID 10 array.
RAID 5 arrays stripe data over the member drives with one parity strip on every stripe. RAID 5 arrays have single redundancy with higher space efficiency than RAID 10 arrays, but with some performance penalty. RAID 5 arrays can tolerate no more than one member drive failure.
RAID 6 arrays stripe data over the member drives with two parity strips on every stripe. A RAID 6 array can tolerate any two concurrent member drive failures.
RAID 10 arrays stripe data over mirrored pairs of drives. RAID 10 arrays have single redundancy. The mirrored pairs rebuild independently. One member out of every pair can be rebuilding or missing at the same time. RAID 10 combines the features of RAID 0 and RAID 1.