Imation DataGuard T5R User Manual download pdf (Page 37)

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 o 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 oers the security of mirrored data provided by RAID 1 plus the added capacity of more than two

physical drives. It also oers 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 oers 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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Imation DataGuard T5R User Manual Page 37

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