Chaparral K5312/K7313 - Manual (Page 140)

G- and K-Series User’s Guide
A-2
RAID 0 arrays do not store redundant data, so they are not true RAID applications. If
one disk fails, the entire array fails and all array data is lost. The fault-tolerance of a
RAID 0 array, therefore, is less than that of any single disk in the array. The term
RAID 0 is widely used for these arrays, however, because they are conceptually similar
to true RAID applications.
RAID 1, RAID 1/O (Mirrored Disks)
In RAID 1 and RAID 1/0 arrays (commonly called mirrored arrays) disks are paired,
with both disks in a pair containing the same data. When data is written to a mirrored
array, it is written twice—once to each disk in the pair. A RAID 1 array has only one
set of paired disks. A RAID 1/0 array has multiple pairs, across which data is striped.
The read performance of RAID 1 arrays can be much better than that of a single disk,
while the write performance is slightly lower. In RAID 1/0 arrays, both read
performance and write performance are better than those of a single disk.
A mirrored array is also highly reliable, because both disks in a pair must fail for the
array to fail. In an array with five pairs of mirrored disks, for example, the array can
maintain its integrity even if five disks fail—as long as each pair is left with one good
disk. The main disadvantage of a mirrored array is its cost. Because all disks must
have a twin, you must use twice the number of disks that actually contribute to the
array capacity. In an eight-disk array, for example, you have only four disks of usable
capacity.
RAID 3
RAID 3 arrays contain redundant information in the form of parity data, which is
calculated block-by-block for all user data. The user data is distributed across all but
one of the disks in the array. The parity data is written exclusively to the parity disk
(also known as the check disk). In the event of a disk failure, the data can be
reconstructed from corresponding data stripes on the remaining disks in the array.
RAID 3 provides excellent I/O performance for applications that require high data
transfer rates such as image processing, video processing, scientific data collection,
batch data processing, or sequential reads and writes.
RAID 3 is not well suited for transaction processing or other applications that require
simultaneous reads and writes.