User manual

Common rAid levelS Supported
RAID
Level Description Performance
RAID 0
Stripe
Data is split evenly across multiple disks, striping with no parity, no mirroring, no error checking and no
redundancy. A disk failure will destroy the array and the probability of failure increases with the number of disk
added to the array. Data blocks 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.
More disks in the array provides higher data transfer rates, but with a greater risk of data loss. Storage space
added to the array by each disk is limited to the size of the smallest disk, so the installed disks should be the same
size. Stripe size is normally a multiple of the hard disk sector size (default 64KB/512 bytes). Useful for non-critical
data that changes infrequently and is frequently backed up where redundancy is unnecessary or irrelevant and
when excellent read/write performance is desirable such as audio or video streaming or editing applications.
Random Read Performance: Very good
Random Write Performance: Very good
Sequential Read Performance: Excellent
Sequential Write Performance: Very good
RAID 1
Mirror
Creates an exact copy (mirroring without parity or striping) of a set of data on two or more disks. Used when
reliability is more important than storage capacity. Can only be as big as the smallest member disk and can only
use an even number of disks. One disk can remain inactive, as a backup and be used to rebuild the mirrored disk.
Random Read Performance: Good
Random Write Performance: Good
Sequential Read Performance: Fair
Sequential Write Performance: Good
RAID 1E
Enhanced
Mirror
RAID 1E offers the security of mirrored data provided by RAID 1 plus the added capacity of more than two
physical drives. It also offers overall increased read/write performance plus the flexibility of using an odd
number of physical drives. With RAID 1E, each data stripe is mirrored onto two physical drives. If one drive fails
or has errors, the other drives continue to function, providing fault tolerance.
The advantage of RAID 1E is the ability to use an odd number of physical drives, unlike RAID 1 and RAID 10. You
can also create a RAID 1E Logical Drive with an even number of physical drives. However, with an even number
of drives, you obtain somewhat greater security with comparable performance using RAID 10. RAID 1E logical
drives consist of three or more physical drives. You can create an array with just two physical drives and specify
RAID 1E. But the resulting logical drive is actually a RAID 1.
Random Read Performance: Very good
Random Write Performance: Very good
Sequential Read Performance: Very good
Sequential Write Performance: Very good
RAID 3
Block
Stripe and
Dedicated
Parity
Uses byte-level striping across multiple disks with a dedicated parity disk. Parity information is sent to a
dedicated parity disk, the failure of any disk (including the parity disk) in the array can be tolerated. The
dedicated parity is a performance bottleneck for random writes especially, because it must be accessed
any time data is written to the array. Performance problems might occur if it is necessary to service multiple
requests simultaneously. I/O operation requires activity on every disk and synchronized spindles.
Random Read Performance: Fair
Random Write Performance: Poor
Sequential Read Performance: Very good.
Sequential Write Performance: Fair to good
RAID 5
Block and
Parity
Stripe
Uses block-level striping with parity data distributed across three or more drives; requires all drives but one to
be present to operate. The array is not destroyed if a single drive fails. If a drive fails, any subsequent reads are
calculated from the distributed parity and the drive failure is unnoticeable to the end user. A single drive failure
reduces performance of the entire array until the failed drive has been replaced and the associated data rebuilt.
Random Read Performance: Excellent
Random Write Performance: Fair
Sequential Read Performance:
Good to very good
Sequential Write Performance: Fair
RAID 6
Block and
Double
Parity
Stripe
Extends RAID 5 by adding an additional parity block. It uses block-level striping with double distributed parity distributed
across all member disks. Provides fault tolerance of two drive failures; the array continues to operate with up to two failed
drives. Makes large RAID groups more practical, especially for high-availability systems. This is important because large-
capacity drives lengthen the time required for recovery from the failure of a single drive. In the event of a single drive
failure, single-parity RAID levels are as vulnerable to data loss as a RAID 0 array until the failed drive is replaced and its
data rebuilt; the amount of time the rebuild takes increases with the size of the drive. Double parity gives time to rebuild
the array without the data being at risk if a single additional drive fails before the rebuild is complete.
Random Read Performance:
Very good to excellent
Random Write Performance: Poor
Sequential Read Performance:
Good to very good
Sequential Write Performance: Fair
RAID 10
Mirror /
Stripe
Mirror + Stripe combines both of the RAID 1 and RAID 0 logical drive types. RAID 10 can increase performance
by reading and writing data in parallel or striping, while protecting data by duplicating it or mirroring. The
Imation DataGuard Appliance implements RAID 10 by creating a data stripe over one pair of disk drives, then
mirroring the stripe over a second pair of disk drives. Some applications refer to this method as RAID 0+1.
The data capacity RAID 10 logical drive equals the capacity of the smallest physical drive times the number
of physical drives, divided by two. In some cases, RAID 10 offers double fault tolerance, depending on which
physical drives fail. RAID 10 arrays require an even number of physical drives and a minimum of four. For RAID
10 characteristics using an odd number of physical drives, choose RAID 1E.
Random Read Performance: Very good
Random Write Performance: Very good
Sequential Read Performance: Very good
Sequential Write Performance: Very good
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