Raid 5; Figure 2-8. Diagram Of A Raid 5 Write - Compaq StorageWorks TM RAID Array 3000 Pedestal Storage Subsystem Hardware User's Manual

RAID Array Controller 2-19

RAID 5

RAID 5 addresses the bottleneck issue for barrages of widely scattered, small
I/O operations. Like RAID 4, RAID 5 breaks up data into chunks, calculates
parity, and then writes the chunks in stripes to the disk drives; saving one drive
one each stripe for the parity data. Unlike RAID 4, however, RAID 5 changes
the parity drive on each stripe. This means, for instance, that a write operation
involving drive 2 on stripe 1 can conceivably take place at the same time as a
write involving drive 3 on stripe 2, since they would be addressing different
parity drives. Figure 2-5 shows a diagram of a RAID 5 write.

Figure 2-8. Diagram of a RAID 5 write

RAID 5 handles drive failures in the same manner as RAID 4, except the
parity is different for each stripe. The controller either uses the parity
information on a stripe to reconstruct its data or simply reads the data as
normal, depending on the location of the stripe's parity drive.