HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning Storage Configurations
2–19HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
2–19
The relationship between the chunk size and the average request size determines if
striping maximizes the request rate or the data-transfer rate. You can set the chunk size
or use the default setting (see “Chunk Size,” page 2–30, for information about setting
the chunk size). Figure 2–6 shows another example of a three-member RAID 0
stripeset.
A major benefit of striping is that it balances the I/O load across all of the disk drives
in the storageset. This can increase the subsystem performance by eliminating the hot
spots (high localities of reference) that occur when frequently accessed data becomes
concentrated on a single disk drive.
Figure 2–6: 3-member RAID 0 stripeset (example 2)
Keep the following points in mind as you plan your stripesets:
• Reporting methods and size limitations prevent certain operating systems from
working with large stripesets.
• A storageset should only contain disk drives of the same capacity. The controller
limits the effective capacity of each member to the capacity of the smallest
member in the storageset (base member size) when the storageset is initialized.
Thus, if you combine 9 GB disk drives with 4 GB disk drives in the same
storageset, you waste 5 GB of capacity on each 9 GB member.
If you need high performance and high availability, consider using a RAIDset,
striped-mirrorset, or a host-based shadow of a stripeset.
Virtual disk
Block 0
Block 1
Block 2
Block 3
Block 4
Block 5
etc.
Disk 1
Block 0
Block 3
etc.
Disk 2
Block 1
Block 4
etc.
Disk 3
Block 2
Block 5
etc.
Operating
system
view
Actual
device
mappings
Stripeset
CXO4592B