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NS170 User Guide - Upgrading your Server
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Standard RAID Types
RAID 0
Also known as 'striping'. Data is written in blocks across multiple drives, so one drive
can be writing (or reading) a block while the next is seeking the next block. The
advantages of striping are the higher access rate, and full utilization of the array
capacity. The disadvantage is there is no fault tolerance - if one drive fails, the entire
contents of the array become inaccessible.
RAID 1
Mirroring provides redundancy by writing twice - once to each drive. If one drive fails,
the other contains an exact duplicate of the data and the controller can switch to using
the mirror drive with no lapse in user accessibility. The disadvantages of mirroring are
no improvement in data access speed, and higher cost, since twice the number of drives
is required (50% capacity utilization).
RAID 5
RAID level 5 provides striping as well as parity for error recovery. The parity block is
distributed among the drives of the array, giving a more balanced access load across the
drives. The parity information is used to recover the data if one drive fails. The
disadvantage is a relatively slow write cycle (2 reads and 2 writes are required for each
block written). The array capacity is N-1, with a minimum of 3 drives required.