RAID-0
Level 0 is not redundant, hence does not truly fit the "R.A.I.D."
acronym. In level 0, information is split across drives, resulting in higher
data throughput. Since no redundant information is stored, performance
is very good, but the failure of any disk in the array results in
information loss. This level is commonly referred to as striping.
RAID-1
Level 1 provides redundancy by writing all information to two or
more drives. The performance of a level 1 array tends to be faster
on reads and slower on writes compared to a single drive, but if
either drive fails, no information is lost. This is a good entry-level
redundant system, since only two drives are required; however, since
one drive is used to store a duplicate of the other, the cost per
megabyte is high. This level is commonly referred to as mirroring.
RAID-5
Level 5 employs a combination of striping and parity checking. The
use of parity checking provides redundancy without the overhead
of having to double disk capacity. Simply put, parity checking involves
determining whether each given block has an odd or even value. These
values are summed across the stripe sets to obtain a parity value.
With this parity value, the contents of a failed drive can easily
be determined and rebuilt on a spare drive.
