Determining A Hot-Spare - Sun Microsystems StorEdge T3+ Installation And Configuration Manual

The following applications benefit most from the RAID controller hardware of the
array:
Data-intensive NFS file system, version 3
DSS
DW
HPC
Note – For more information about RAID levels, see "Using RAID Levels to
Configure Redundancy" on page 123.

Determining a Hot-Spare

A hot-spare is always optional. Disk drive nine is always used as the hot-spare. If
you choose to include a hot-spare in your configuration and you want it available
for the first volume, you must specify it when you create the first volume in an array.
This is also true if you create a second volume. If you want to add a hot spare at a
later date to an existing volume, you must first delete that volume and then recreate
it with the hot-spare designated during creation.
Note – Only one hot spare is allowed per array and it is only usable for the array in
which it is configured. The hot spare must be configured as drive 9.
During a failure, for example, should drive 7 fail, drive 9 is synchronized
automatically with the entire LUN to reflect the data on drive 7. After the failed
drive (7) is replaced, the controller unit will automatically copy the data from drive 9
to the new drive, and drive 9 will become a hot spare again.
Tip – Although they are not required, hot spares are always recommended for
mission-critical configurations because they allow the controller unit to reconstruct
the data from the RAID group and only take a performance hit while the
reconstruction is taking place. If a hot spare is not used, the controller unit remains
in write-through cache mode until the failed drive is replaced and reconstruction is
complete (which could take an extended period of time). During this time, the array
is operating in degraded mode.
If no hot spare is present, the reconstruction of the data will begin when the failed
drive is replaced—provided RAID 1 or RAID 5 is used.
Chapter 8 Post-Installation Global Parameters Configurations 121