APC RAID Subsystem SCSI-SATA II User Manual download pdf (Page 35)

SCSI to SATA II RAID Subsystem

User Manual

Definition of RAID Levels

RAID 0 is typically defined as a group of striped disk drives without parity or data

redundancy. RAID 0 arrays can be configured with large stripes for multi-user

environments or small stripes for single-user systems that access long sequential

records. RAID 0 arrays deliver the best data storage efficiency and performance of any

array type. The disadvantage is that if one drive in a RAID 0 array fails, the entire array

fails.

RAID 1, also known as disk mirroring, is simply a pair of disk drives that store duplicate

data but appear to the computer as a single drive. Although striping is not used within a

single mirrored drive pair, multiple RAID 1 arrays can be striped together to create a

single large array consisting of pairs of mirrored drives. All writes must go to both drives

of a mirrored pair so that the information on the drives is kept identical. However, each

individual drive can perform simultaneous, independent read operations. Mirroring thus

doubles the read performance of a single non-mirrored drive and while the write

performance is unchanged. RAID 1 delivers the best performance of any redundant array

type. In addition, there is less performance degradation during drive failure than in RAID

5 arrays.

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APC RAID Subsystem SCSI-SATA II User Manual Page 35