Glossary
Array
As used in RAID, an array consists of
one or more hard drives which are logically combined to form a single storage
drive. Arrays are categorized by the method in which they are accessed to
logically organize data on them for purposes of performance enhancement,
capacity augmentation, and /or data redundancy protection. The different types
of arrays include RAID 0 (Striping), RAID 1 (Mirroring), RAID 0/1 (Mirrored
Striping), RAID 1/0 (Striped Mirroring), RAID 5, etc.
Controller
A system may include RAID Controllers. They provide RAID 0, RAID 1, RAID 0/1, JBOD, Spare and Hot Swap functions. There are two channels on each controller. One is channel 0 (Primary Channel) and the other is channel 1 (Secondary Channel).
Channel
A bus
that uses some protocol to move data to/ from the disks.
The
channel provides a connection between controller and devices (Array or physical
disk). Each channel can attach a master device and a slave device.
Hot Swap
To pull
out a component from a system and plug in a new one while the power is still on
and the unit is still operating. Note:
Ensure that your system supports hot swappable drives before executing this
operation.
JBOD (Volume)
JBOD is
an acronym for Just a Bunch of Disks. It is used to refer to hard disks that
are not configured according to RAID -- a subsystem of disk drives that
improves performance and fault tolerance.
JBOD provides much more capacity (the sum of all the disks). If there is
more than one single physical disk (not member of an array and not an ATAPI
device or a removable disk), you can create a JBOD array.
Mirroring
It
refers to a data protection technique that duplicates data from one drive to
another. This is known as RAID Level 1.
RAID
Redundant
Array of Independent Disks (RAID) refers to a method of organizing data on one
or more physical disks to provide increased I/O performance and data
protection. The different methods for organizing the data are referred to as
RAID Levels.
RAID 0
(Striping)
RAID 0
is typically defined as a group of striped disk drives without parity or data
redundancy. RAID 0 arrays can be configured with large stripes for multi-user environments
or small stripes for single-user systems that access long sequential records.
RAID 0 arrays deliver the best data storage efficiency and performance of any
array type. The disadvantage is that if one drive in a RAID 0 array fails, the
entire array fails.
RAID 1
(Mirroring)
Also known as mirroring.
Mirroring refers to the 100% duplication of data from one disk to another. Due to 100% duplication, this is a
costly solution.
RAID 0/1
(Mirrored Striping)
A
combination of RAID 1 and RAID 0. RAID 0/1 can provide much more speed and
security. Only when four single physical disks are available, you can create a
RAID 0/1 array.
Stripe
A stripe
is interleaved data across multiple drives in an array. Data is sequentially
stored in allocated sizes across disks, based on the RAID level. Stripe size is
the number of drives x the strip size.
Stripe Size
Stripe
size is the size of the logically contiguous data block recorded on all drives connected
to the controller. A variable stripe size allows for the configuration of the
stripe size. The stripe size for a volume can be configured to one of several
sizes (16k, 32k or 64k).