Compaq HSZ80 manual Considerations for Planning a Stripeset, 10Creating Storagesets

3–10Creating Storagesets

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’s performance by eliminating the hot spots, or high localities of reference, that occur when frequently accessed data becomes concentrated on a single disk drive.

Considerations for Planning a Stripeset

Keep the following points in mind as you plan your stripesets:

■A controller can support up to 45 storagesets, consisting of stripesets, mirrorsets and RAIDsets (see Table 3–1).

■Reporting methods and size limitations prevent certain operating systems from working with large stripesets. See the HSZ80 Array Controller ACS Version 8.3 Release Notes or the Quick Setup Guide that came with your software platform kit for details about these restrictions.

■A storageset should only contain disk drives of the same capacity. The controller limits the capacity of each member to the capacity of the smallest member in the storageset when the storagest is initialized (the base member size). Thus, if you combine 9 GB disk drives with 4 GB disk drives in the same storageset, the 4 GB disk drive will be the base member size and you will 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.

NOTE: A striped mirrorset cannot be created if the mirrorsets are enabled for

DT_SUPPORT.

■Striping does not protect against data loss. In fact, because the failure of one member is equivalent to the failure of the entire stripeset, the likelihood of losing data is higher for a stripeset than for a single disk drive.

For example, if the mean time between failures (MTBF) for a single disk is one hour, then the MTBF for a stripeset that comprises N such disks is l/N hours. As another example, if a single disk’s MTBF is 150,000 hours (about 17 years), a stripeset comprising four of these disks would only have an MTBF of slightly more than four years.