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IOMEGA STORAGE PROVISIONING AND RAID MIGRATION CONFIGURATION GUIDE
Level
RAID 5
RAID 6
Description
Striped set with distributed parity or interleave parity.
Distributed parity requires all drives but one to be present to
operate; drive failure requires replacement, but the array is not
destroyed by a single drive failure. Upon drive failure, any
subsequent reads can be calculated from the distributed parity,
such that the drive failure is masked from the end user. The
array will have data loss in the event of a second drive failure
and is vulnerable until the data that was on the failed drive is
rebuilt onto a replacement drive. A single drive failure in the
set will result in reduced performance of the entire set until
the failed drive has been replaced and rebuilt.
Striped set with dual distributed parity. Provides fault
tolerance from two drive failures; array continues to operate
with up to two failed drives. This makes larger RAID groups
more practical, especially for high availability systems. This
becomes increasingly important because large-capacity
drives lengthen the time needed to recover from the failure
of a single drive. Single parity RAID levels are vulnerable to
data loss, until the failed drive is rebuilt: the larger the drive,
the longer the rebuild will take. Dual parity gives time to
rebuild the array without the data being at risk if a (single)
additional drive fails before the rebuild is complete.
Min. #
of Disks
3
4
Space
Efficiency
n-1
n-2
Fault
Tolerance
1 disk
2 disks
Image
A1
B1
C1
D
p
RAID 5
A2
B2
C
p
D1
A3
B
p
C2
D2
Aq
B3
C3
D3
A1
B1
C1
Eq
RAID 6
Note: Due to parity calculation, write performance could be greatly impacted. Therefore, as a best practice, it is
recommended to create RAID 5 using at least 4 drives and RAID 6 using at least 6 drives.
Note: Typically a RAID 10 group consists of an even number of drives. On an Iomega px12-350r, RAID 10 can
be created using an odd number of drives. Each data block is repeated n times in a k-way stripe. The layout is
equivalent to the standard RAID 10 layout, but it does not require that n divides k. For example, an n2 layout on
2, 3, 4 drives would look like:
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D
p
A2
B2
C
p
E1
Dq
A3
B
p
Cq
E2
D1
A
p
Bq
C2
E3
D2
Aq
B3
C3
E
p
D3
A1
A2
A3
A4
A1
A2
A3
A4
A1
A2
A4
A5
A1
A3
A4
A6
A2
A3
A5
A6
A1
A3
A5
A7
A1
A3
A5
A7
A2
A4
A6
A8
A2
A4
A6
A8
2 Drives 3 Drives 4 Drives
DISK 0 DISK 1 DISK 2 DISK 3
DISK 0 DISK 1 DISK 2 DISK 3 DISK 4