Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Compaq Tru64 UNIX Installation and Configuration Guide

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Figure 2–11. A five member RAIDset using parity
RAIDsets are similar to stripesets in that the I/O requests are broken into smaller
“chunks” and striped across the disk drives. RAIDsets also create chunks of parity data
and stripe them across all the members of the RAIDset. This parity data is derived
mathematically from the I/O data and enables the controller to reconstruct the I/O data
if a single disk drive fails. Thus, it becomes possible to lose a disk drive without losing
access to the data it contained. Data could be lost, however, if a second disk drive fails
before the controller replaces the first failed disk drive and reconstructs the data.
The relationship between the chunk size and the average request size determines if
striping maximizes the request rate or the data-transfer rates. You can set the chunk
size or use the default setting. See “Chunk Size,” page 2–23, for information about setting
the chunk size.
Keep these points in mind when planning RAIDsets:
■ Reporting methods and size limitations prevent certain operating systems from
working with large RAIDsets.
■ Both cache modules must be the same size.
Virtual disk
Block 0
Block 1
Block 2
Block 3
Block 4
Block 5
etc.
Disk 1
Block 0
Block 5
Block 10
Block 15
Disk2
Block 1
Block 6
Block 11
Parity 12-15
Disk 3
Block 2
Block 7
Parity 8-11
Block 12
Disk 4
Block 3
Parity 4-7
Block 8
Block 13
Disk 5
Parity 0-3
Block 4
Block 9
Block 14
Operating
system
view
RAIDset
CXO6463B