Global Hot Spares; Setting Stripe Segment Size - HP Surestore Disk Array 12h - And FC60 Service Manual

•
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.
•
If you choose to limit the number of global hot spares, make sure you are able to
respond quickly to replace a failed disk. If an operator is always available to replace a
disk, you may not need the added protection offered by multiple global hot spares.

Setting Stripe Segment Size

Another factor you may have to consider is the stripe segment size you use for a volume.
The stripe segment size determines how much data is written to a disk before moving to
the next disk in the volume to continue writing. For example, if the stripe segment size is
set to 4 bytes, the disk array will write 4
K
disk 2, then 4 bytes of data to disk 3, and so on. For more information, see
K
on page 47.
When creating a volume, the default value used for the stripe segment size is the value
currently set for the cache page size (4
4 bytes.
K
Managing Disk Array Capacity
194
bytes of data to disk 1, then 4
K
bytes or 16 bytes). The default cache page size is
K K
bytes of data to
K
"Data Striping"