Windows Server Troubleshooting - RAID

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RAID levels and their fault tolerance

Although there are many different RAID levels, levels 2, 3, 4, and 6 are rarely used and not supported by Windows.

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 Superseded by RAID 3.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