Using Raid5 - HP StorageWorks XP48 - Disk Array Owner's Manual

Using RAID5

RAID Technology
RAID5, like RAID3, processes data between two or more disk drives
simultaneously. RAID5 also saves parity information to a separate disk
drive.
RAID5, unlike RAID3, saves information as blocks of data, which allows
the RAID controller to access each disk for only one stripe of data. This
also allows RAID5 to perform input/output operations on other disks in
parallel. By saving the data as small blocks, this approach permits increased
I/O performance. This makes RAID5 ideal for transaction processing.
In large-scale (sequential) input/output operations, RAID5 permits parallel
processing of the parity blocks, which increases the data transfer rate.
In small-scale input/output operations though, RAID5 must perform extra
read operations from the data and parity disks. This slows the transfer rate
and is called write penalty. To limit this problem, RAID5 distributes the
parity data on several disks in the parity group.
RAID Controller
A B C
A B
E F
I G-I
J-L J
Figure 15. RAID5 Disk Array
Data (block)
A B C D
Parity
Generator
Circuit
C A-C
D-E D
G H
K L
99