Configuration: Disk Groups and Virtual Disks 123

Hot Spares and Rebuild

A valuable strategy to protect data is to assign available physical disks in the
storage array as hot spares. A hot spare adds another level of fault tolerance to
the storage array.
A hot spare is an idle, powered-on, stand-by physical disk ready for immediate
use in case of disk failure. If a hot spare is defined in an enclosure in which a
redundant virtual disk experiences a physical disk failure, a rebuild of the
degraded virtual disk is automatically initiated by the RAID controller
modules. If no hot spares are defined, the rebuild process is initiated by the
RAID controller modules when a replacement physical disk is inserted into
the storage array.

Global Hot Spares

The MD3200i series supports global hot spares. A global hot spare can replace
a failed physical disk in any virtual disk with a redundant RAID level as long
as the capacity of the hot spare is equal to or larger than the size of the
configured capacity on the physical disk it replaces, including its metadata.

Hot Spare Operation

When a physical disk fails, the virtual disk automatically rebuilds using an
available hot spare. When a replacement physical disk is installed, data from
the hot spare is copied back to the replacement physical disk. This function is
called copy back. By default, the RAID controller module automatically
configures the number and type of hot spares based on the number and
capacity of physical disks in your system.
A hot spare may have the following states:
• A standby hot spare is a physical disk that has been assigned as a hot spare
and is available to take over for any failed physical disk.
• An in-use hot spare is a physical disk that has been assigned as a hot spare
and is currently replacing a failed physical disk.

Hot Spare Drive Protection

You can use a hot spare physical disk for additional data protection from
physical disk failures that occur in a RAID Level 1, or RAID Level 5 disk
group. If the hot spare physical disk is available when a physical disk fails, the
RAID controller module uses redundancy data to reconstruct the data from
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