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IOMEGA STORAGE PROVISIONING AND RAID MIGRATION CONFIGURATION GUIDE
9
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Level
RAID 0
RAID 1
RAID 10
Description
Striped set without parity or Striping. Provides improved
performance and additional storage but no redundancy
or fault tolerance. Because there is no redundancy, this
level is not actually a Redundant Array of Inexpensive
Disks, i.e. not true RAID. However, because of the
similarities to RAID (especially the need for a
controller to distribute data across multiple disks),
simple stripe sets are normally referred to as RAID 0.
Any disk failure destroys the array, which has greater
consequences with more disks in the array (at a
minimum, catastrophic data loss is twice as severe
compared to single drives without RAID). A single disk
failure destroys the entire array because when data is
written to a RAID 0 drive, the data is broken into
fragments. The number of fragments is dictated by the
number of disks in the array. The fragments are written to
their respective disks simultaneously on the same sector.
This allows smaller sections of the entire chunk of data to
be read off the drive in parallel, increasing bandwidth.
RAID 0 does not implement error checking so any error
is unrecoverable. More disks in the array means higher
bandwidth, but greater risk of data loss.
Mirrored set without parity or Mirroring. Provides fault
tolerance from disk errors and failure of all but one of
the drives. Increased read performance occurs when
using a multi-threaded operating system that supports
split seeks, as well as a very small performance reduction
when writing. Array continues to operate so long as at
least one drive is functioning. Using RAID 1 with a
separate controller for each disk is sometimes called
duplexing.
Striped set of mirrors. Provides both disk replication
and data sharing by combining the benefits of RAID 0
and RAID 1.
Min. #
of Disks
2
2
4
Space
Efficiency
n
1
(size of the
smallest disk)
n/2
Fault
Tolerance
0 (none)
n-1 disks
n/2 disks,
one from
each mirror
set
A1
DISK 0
A3
A5
A7
RAID 0
A2
DISK 1
A4
A6
A8
A1
DISK 0
A2
A3
A4
RAID 1
A1
DISK 1
A2
A3
A4
A1
A3
A5
A7
RAID 1
RAID 10
RAID 0
A1
A3
A5
A7
A2
A4
A6
A8
RAID 1
A2
A4
A6
A8
The following table compares the different RAID levels. For more details, refer to http://en.wikipedia.org/wiki/RAID.