Global Hot Spares - HP Surestore Disk Array 12h - And FC60 Advanced User's Manual

the RAID level used by a LUN, you must unbind the LUN and rebind it using the new RAID
level.
With the exception of RAID 0, all RAID levels supported by the disk array provide
protection against disk failure. However, there are differences in performance and storage
efficiency between RAID levels. For more information on RAID levels and their
comparative operating characteristics, see
The two factors that will influence the RAID level you select are performance and storage
efficiency.
•
Performance - The performance characteristics differ for each RAID level. The types
of applications you are running and the I/O activity associated with them should
influence the RAID level you select for a LUN. The performance characteristics for each
RAID level are summarized in
•
Storage Efficiency - the storage efficiency can range from 50% for RAID 1 and 0/1 up
to > 80% for RAID 5. The higher the efficiency, the less cost per megabyte for storing
your data.

Global Hot Spares

Global hot spares provide additional protection against disk failures. The number of global
hot spares you use will reflect how much protection you need. Each global hot spare you
add will provide protection against the failure of a single disk. In addition to restoring
hardware redundancy, a global hot spare also restores disk array performance that may be
diminished while the disk array is operating in degraded mode with a failed disk.
When adding global hot spares, consider the following:
•
It is recommended that you add one global hot spare per disk channel. This provides
maximum protection against disk failure. A global hot spare can be used to replace any
failed disk within the array, regardless of what channel it is on.
•
When a failed disk is replaced, the data will be copied from the global hot spare disk to
the replacement disk and the global hot spare will again be available as protection
against another disk failure.
Managing Disk Array Capacity
248
"RAID Technology" on page
"RAID Level Comparisons" on page
47.
57.