Raid 5 Arrays - Adaptec CDP-00277-01-A Installation And User Manual

RAID 5 Arrays

A RAID 5 array is built from a minimum of three disk drives, and uses data striping and parity data to
provide redundancy. Parity data provides data protection, and striping improves performance.
Parity data is an error-correcting redundancy that's used to re-create data if a disk drive fails. In RAID
5 arrays, parity data (represented by Ps in the next figure) is striped evenly across the disk drives with
the stored data.
Drive segment size is limited to the size of the smallest disk drive in the array. For instance, an array
with two 250 GB disk drives and two 400 GB disk drives can contain 750 GB of stored data and 250 GB
of parity data, as shown in this figure.
Disk Drive 1 250 GB
Disk Drive 2 250 GB
Disk Drive 3 400 GB
Disk Drive 4 400 GB
Disk Drives in Logical Drive
Proprietary and Confidential to PMC-Sierra, Inc.
Document No.: CDP-00277-01-A Rev. A, Issue:
Serial Attached SCSI RAID Controllers Installation and User's Guide
Drive Segment Size
(Smallest Disk Drive)
1 4 . . .
Disk Drive 1
2 5 . . .
Disk Drive 2
3 P . . .
Disk Drive 3
P 6 . . .
Disk Drive 4
RAID 5 Logical Drive = 750 GB plus Parity
P
748
749
Unused Space = 150 GB
750
Unused Space = 150 GB
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