Page 1299 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

after one of the disks fails. Some of the common RAID configurations
are as follows:

RAID-0 This is also called striping. It uses two or more disks and

improves the disk subsystem performance, but it does not provide
fault tolerance.

RAID-1 This is also called mirroring. It uses two disks, which both
hold the same data. If one disk fails, the other disk includes the data so
a system can continue to operate after a single disk fails. Depending on
the hardware used and which drive fails, the system may be able to
continue to operate without intervention, or the system may need to

be manually configured to use the drive that didn’t fail.

RAID-5 This is also called striping with parity. It uses three or more
disks with the equivalent of one disk holding parity information. If any
single disk fails, the RAID array will continue to operate, though it will
be slower.

RAID-10 This is also known as RAID 1 + 0 or a stripe of mirrors, and

is configured as two or more mirrors (RAID-1) configured in a striped
(RAID-0) configuration. It uses at least four disks but can support
more as long as an even number of disks are added. It will continue to
operate even if multiple disks fail, as long as at least one drive in each
mirror continues to function. For example, if it had three mirrored sets
(called M1, M2, and M3 for this example) it would have a total of six
disks. If one drive in M1, one in M2, and one in M3 all failed, the array

would continue to operate. However, if two drives in any of the
mirrors failed, such as both drives in M1, the entire array would fail.

Fault tolerance is not the same as a backup. Occasionally,

management may balk at the cost of backup tapes and point to the
RAID, saying that the data is already backed up. However, if a
catastrophic hardware failure destroys a RAID array, all the data is
lost unless a backup exists. Similarly, if an accidental deletion or
corruption destroys data, it cannot be restored if a backup doesn’t
exist.