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RAID Array Controller 2-19
Compaq Confidential – Need to Know Required
Writer: Bob Young Project: RAID Array 3000 Pedestal Storage Subsystem Hardware User’s Guide Comments:
Part Number: EK-SMCPO-UG. C01 File Name: c-ch2 RAID Array Controller.doc Last Saved On: 12/4/00 1:51 PM
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.