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 RAID 5 Definition
We define RAID 5 |
RAID 5 - A RAID 5 configuration utilizes three or more hard drives and stripes the data across them, much like RAID 0. The difference is that parity information is striped across the drives as well, so if you lose any one drive the information can be reconstructed from the parity information. For example, with three drives the first stripe is data (on drive 1), data (on drive 2), parity (on drive 3); then data, parity, data; then parity, data, data. This pattern continues. If one drive fails, you get a mix of parity and data on the remaining two drives, and you can reconstruct all of the data. Of course, before the data is reconstructed the RAID operates in "degraded mode" and is slow. To reconstruct the data you must remove the failed drive and replace it with another, or use a "hot spare." During reconstruction the array continues to be slow. Once the RAID is reconstructed performance returns to normal levels. RAID 5 performance is similar to RAID 0 performance, but a bit slower due to the parity information. Performance increases, like RAID 0, when more drives are added. With RAID 5 you get most of the space that you've paid for, minus one drive's worth. A common option with RAID 5 is the hot spare, where a drive sits idle until needed. If you lose a drive, the hot spare takes over and the RAID is rebuilt automatically. Of course you still get the performance penalty during the rebuilding stage, but it can be set to happen automatically. |
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