Sun Microsystems Sun StorEdge T3 - Manual (Page 31)

Chapter 2 Configuring Global Parameters 19
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.
Drive 9 will be the hot spare in the unit. So, for example, should a drive failure occur
on drive 7, drive 9 is synchronized automatically with the entire LUN to reflect the
data on drive 7. Once 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 there is no hot spare, the reconstruction of the data will begin when the failed
drive is replaced, provided RAID 1 or RAID 5 is used.
Creating and Labeling a Logical Volume
You must set the RAID level and the hot-spare disk when creating a logical volume.
For the Solaris operating system to recognize a volume, it must be labeled with the
format
or fmthard command.
Caution – Removing and reconfiguring a logical volume will destroy all data
previously stored there.
Setting the LUN Reconstruction Rate
Note – When a failed drive is disabled, the volume is operating without further
redundancy protection, so the failed drive needs to be replaced as soon as possible.