[ Thanks for this link to Jeremy C. Reed, who notes that this
is “…Not necessarily a Linux article — but it has some great
descriptions of RAID terminology and usage.” ]
“RAID is an acronym for “Redundant Array of Inexpensive
Disks”. The purpose of RAID is both to join more than one disk into
a single logical device and to prevent a single physical disk
failure from causing the entire logical device to fail.”
“RAID 0 is also known as striping. It simply consists of joining
two or more disks into a larger logical device. It does not provide
any redundancy in itself, but is commonly used to combine RAID sets
utilizing other RAID levels, such as RAID 1 or RAID 5. A striped
RAID 1 set is known as RAID 0+1 or RAID 10. Likewise, a striped
RAID 5 is known as RAID 0+5 or RAID 50. RAID 1 is also known as
mirroring. Two disks are combined — each contain the same data. If
one disk fails, the other continues on and the logical device
remains available.”
“RAID 4 combines three or more disks into a single device with
one of the disks dedicated to parity. If one disk fails, the
logical device will remain available, but with degraded
performance. This RAID level is not commonly used because the
single parity disk introduces a considerable bottleneck for writes.
RAID 5 combines three or more disks into a single device with the
parity distributed across each drive in the set. If one disk fails,
the logical device will remain available, but with degraded
performance.”