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RAID SYSTEM and MODES
A Redundant Array of Independent (or Inexpensive) Disks (RAID) is a system
that utilizes multiple hard drives to share or replicate data among the disks. The
benefit, depending on the selected RAID Mode (combinations of disks), is one or
more of increased data integrity, fault-tolerance, throughput or capacity when
compared to single drives.
JBOD
Just a Bunch of Disks (JBOD) refers to a group of hard drives. In JBOD, the
number of logical drives is equal to the number of physical drives. This mode
allows the RAID System to operate as a multi-disk storage enclosure, but
provides no data redundancy.
In JBOD mode, if one disk in the RAID System fails, all data in that disk will
be lost. However, the data in the second disk is still accessible.
SPANNING
Spanning provides another maximum capacity solution. Spanning combines
multiple hard drives into a single logical unit. Unlike Striping, Spanning writes
data to the first physical drive until it reaches full capacity. When the first disk
reaches full capacity, data is written to the second physical disk. Spanning
provides the maximum possible storage capacity but does not increase
performance.
Data
A
B
C
D
E
F
G
H
In Spanning mode, if one disk in the RAID System fails, all data in that disk
will be lost. However, the data in the second disk is still accessible.
Host
Read/ Write
READ
RAID
CONTROLLER
WRITE
Hard Disk
9GB
A
B
C
D
+
=
9GB
E
F
G
H
Physical Drive
48
RAID
18GB
A
B
C
D
E
F
G
H
Logical Drive
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