RAID and Subsystem Architectures
RAID is the ability to read or write data across multiple spindles. It uses
internal memory in each disk to avoid waiting whilst the heads are positioned
to the correct track and the disk rotates so the required sector is accessible by
RAID 0, 4, 5 and 6 all use block level striping
An individual disk would contain the 512 Bytes typically associated with
a block command stored on one sector.
This is often referred to as INDEPENDENT ACCESS as an individual
block could be read from or written to an individual disk without
accessing the other drives in the stripe set.
If an individual block is written to however, the parity block(s) will still
need to be updated for RAID 4, 5 and 6. This could create a hot spot
with fixed parity solutions and that is why most vendors chose to
implement distributed parity solutions, unless they could guarantee that
the entire stripe would be written to each time.
Slightly higher write overhead when compared to RAID 2 or 3