|
RAID Level |
Description |
Fault Tolerance |
Performance |
Cost |
|
0—Striping |
Data is striped across the RAID set of disks |
None. If one disk fails,
the data is lost. |
««Excellent. The fastest
RAID level. |
N - Equivalent to
the cost of disks in a non-RAID system |
|
1—Mirroring Duplexing, if
2 RAID controllers are used |
Identical data is written
simultaneously to 2 disks |
«««Excellent.
failover can occur immediately. |
«Very good. Reads bit
faster than it writes. |
˝ N
The most expensive level. |
|
2 |
All data is striped across both data and parity
disks. All disks must be accessed in parallel. |
«Good. |
Superseded by RAID 3. |
Approaching ˝ N |
|
3—Striping + parity drive |
Similar to RAID 2, but
parity data is stored on a dedicated drive. |
««Very good, but all fault tolerance is lost if the
parity drive fails. |
Moderate. |
N/(N-1) |
|
4 - Block-level parity
with a dedicated parity disk |
Similar to RAID 3, but with multiple independent
disk reads instead of synchronized read & writes to the array |
««Very
good. |
Moderate. |
N/(N-1) |
|
5—Distributed data
guarding |
Instead of a dedicated parity drive, data and
parity information is interleaved over all drives in the array. |
«««Excellent.
Array failure only when 2 drives fail. |
«Read: excellent. Write:
slower |
N/(N-1) |
|
6 |
RAID 5 + extra parity
information |
««««Best.
Array failure only when 3 drives fail |
Similar to RAID 5, but
writes are a bit slower. |
(N/(N-1))+N |
|
10-Striped mirrored disks |
RAID 0, but with mirrored
pairs instead of single drives. |
«««Excellent.
Array failure only when 2 drives fail. |
«fastest on
reads; almost as fast on writes. |
˝ N
|
