RAID (redundant array of independent disks; originally redundant array of
inexpensive disks) is a way of storing the same data in different places
(thus, redundantly) on multiple hard disks. By placing data on multiple
disks, I/O operations can overlap in a balanced way, improving performance.
Since multiple disks increases the mean time between failure (MTBF), storing
data redundantly also increases fault-tolerance.
A RAID appears to the operating system to be a single logical hard disk.
RAID employs the technique of striping, which involves partitioning each
drive's storage space into units ranging from a sector (512 bytes) up to
several megabytes. The stripes of all the disks are interleaved and addressed
in order.
In a single-user system where large records, such as medical or other
scientific images, are stored, the stripes are typically set up to be small
(perhaps 512 bytes) so that a single record spans all disks and can be
accessed quickly by reading all disks at the same time.
In a multi-user system, better performance requires establishing a stripe
wide enough to hold the typical or maximum size record. This allows
overlapped disk I/O across drives.
There are at least nine types of RAID plus a non-redundant array (RAID-0):
RAID-0. This technique has striping but no redundancy of data. It offers the
best performance but no fault-tolerance.
Given the above, there is little to choose between various chips sets. Does
the manufacturer show a preference for RAID 0 with 2 HDDs in the user
manual. They must have some reason for providing two chips sets.
