A disk array consists
of multiple disk drives under the command of an array controller.
The disk array incorporates features that differentiate it from traditional
disk storage devices.
Most types of disk arrays provide for one of two
possible options for protecting data in the event of a disk failure.
This becomes more and more important as the number of disks on a system
increases, since the chance of a disk failure also increases. Normally,
a disk crash brings the system down or prevents access to data, removing
it from service until the problem is located and repaired, and the
data is reloaded.
The first kind of data protection is called data encoding. When a disk drive fails, the
array controller generates encoded data, which is similar to parity
or checksum calculations. This allows missing user data to be reconstructed
using a mathematical formula to rebuild lost data. As a result, the
data remains accessible and the system remains up and running without
suffering any downtime.
The second method of data protection utilizes hardware mirroring as a means of providing
high data availability by duplicating data on redundant disk drives.
As a result, failure in one disk still allows access to the data on
an alternate disk.