| |
Spare
& Standby Drives
Spare
or standby drives are simply unused disk drives that are connected
to the same controller as the other members of a logical drive and
may be used to replace one of the existing drives in the event of
failure. Most hardware controllers do not require the standby drive
to be connected to the same I/O bus or power supply, and it may
be physically located anywhere as long as it is physically connected
to the controller. The controller must be aware that it may use
the unused drive in the event of a member drive failing, and this
is achieved and power supply as the other of the
Local Spare Drives
Controllers that support Local spare drive allocation offer the
option to dedicate a specific drive to a specific logical drive
or volume. This is handy for situations where one array is of critical
importance but another array attached to the controller can be left
with a missing drive until a new one is manually installed. If the
spare was used on the less important array and a drive was lost
on the critical array before another replacement drive was installed,
no spare would be available to automatically rebuild the critical
array.
The use of Local spare drives also allows different hard drives
of varying capacities to be allocated to arrays containing drives
of equal or less capacity. The controller will not attempt to initialise
an incompatible or unsuitable drive.
Global Spare Drives
Global spare drives are the opposite of Local spare drives. They
are drives that are publicly available to the controller for use
on any array which suffers a drive failure or error. Specifying
both a Local drive for a specific logical drive together with having
a Global drive available across all logical drives increases the
level of protection against drive failure. Only if two drives in
the same array fail simultaneously or before a rebuild is complete
will result in data loss.
Systems that support a Hot-swap function
may allow the addition of a new local or global spare drive after
the logical drive is built and is already running without stopping
any I/O processing or taking the system off-line.
Related
topics:
|
