Toshiba Magnia 560S - Manual (Page 34)

RAID Overview 16
Introduction to RAID
Parity
Parity generates a set of redundancy data from two or more parent data sets. The
redundancy data can be used to reconstruct one of the parent data sets. Parity data does
not fully duplicate the parent data sets. In RAID, this method is applied to entire drives
or stripes across all disk drives in an array.
Table 2.3 describes distributed parity, which is used in RAID 5.
Table 2.3 Distributed Parity
Type Description
Distributed Parity The parity data is distributed across all drives in the
system.
If a single disk drive fails, it can be rebuilt from the parity and the data on the remaining
drives.
RAID 5 combines distributed parity with disk striping. Parity provides redundancy for
one drive failure without duplicating the contents of entire disk drives, but parity
generation can slow the write process.
Hot Spares
A hot spare is an extra, unused disk drive that is part of the disk subsystem. It is usually
in standby mode, ready for service if a drive fails. Hot spares permit you to replace
failed drives without system shutdown or user intervention.
RAID Controller Kit-G implements automatic and transparent rebuilds using hot spare
drives, providing a high degree of fault tolerance and zero downtime. The RAID
Controller Kit-G RAID Management software allows you to specify physical drives as
hot spares. When a hot spare is needed, the RAID Controller Kit-G controller assigns
the hot spare that has a capacity closest to and at least as great as that of the failed drive
to take the place of the failed drive.
NOTE: Hot spares are employed only in arrays with redundancy, for example,
RAID levels 1, 5, 10, and 50.
A hot spare connected to a specific RAID Controller Kit-G controller can be
used only to rebuild a drive that is connected to the same controller.
Hot Swap
A hot swap is the manual replacement of a defective physical disk unit while the
computer is still running. When a new drive has been installed, you must issue a
command to rebuild the drive.