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RAID Levels
This appendix provides a functional description of Redundant
Array of Independent Disks (RAID). This includes information
about RAID and available RAID levels.
RAID Description
Redundant Array of Independent Disks (RAID) is a storage
technology used to improve the processing capability of storage
systems. This technology is designed to provide reliability in
disk array systems and to take advantage of the performance
gains multiple disks can offer.
RAID comes with a redundancy feature that ensures fault-
tolerant, uninterrupted disk storage operations. In the event of a
disk failure, disk access will still continue normally with the
failure transparent to the host system.
RAID has six levels: RAID 0 ~ 5. RAID levels 1, 3 and 5 are
the most commonly used levels, while RAID levels 2 and 4 are
virtually never used. The following sections described in detail
each of the commonly used RAID levels.
Non-RAID Storage
One common option for expanding disk storage capacity is
simply to install multiple disk drives into the system and then
combine them end to end. This method is called disk spanning.
In disk spanning, the total disk capacity is equivalent to the sum
of the capacities of all SCSI drives in the combination. This
combination appears to the system as a single logical drive.
Thus, combining four 1GB SCSI drives in this way, for example,