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## RAID Arrays

### Dialog box "Construct RAID"

A tool to construct virtual RAIDs using individual disks (or partitions and images) when it is not possible to use standard tools of the controller (hardware RAID) or the operating system (software RAID).

If it is necessary disks must be detached from the RAID controller and attached to a computer as single disks.

Incorrect selection of a RAID type or data rotation (striping) leads to incorrect data recovery (despite that the directory structure may be reconstucted correctly).

### RAID types

RAID-0. Usually contains two disks on which information is written alternately by blocks (stripes). If one disk is absent only small files which fit into single block may be recovered. RAID-0 is supported in read/write mode.

RAID-1. Usually contains two disks, data is duplicated. Stripe size is not used. Supported in read-only mode. One healphy disk may be opened as a single device without loss of data.

RAID-4. Usually contains three disks. One disk is for parity. Data is alternated between the rest disks. It is possible to recover all data without any one of the disks. Use NULL device instead of the absent device. Supported in read-only mode.

RAID-5. Usually contains three disks (or more). Data is alternated between all disks herewith one block of parity per the rest blocks of data. There are four types of data rotation on a RAID-5. Some RAIDs (usually hardware) may have delayed parity. It is possible to recover all data without any one of the disks (which should be replace with NULL device). Supported in read-only mode.

RAID-6. Usually contains four disks (or more). It is similar to RAID-5 with exception that two blocks of parity (different types) are used. Only type of parity is supported so only one disk may be replaced with NULL device. Read-only.

RAID: Custom rotation. You may define your own striping (use Menu - Striping...). Use integer numbers from 0 to specify data blocks according to their order on disks, -1 to specify XOR-parity block, and -2 to specify unused block.

E.g. for the diagram:
Disk#0 | Disk#1 | Disk#2 | Disk#3
A1 | A2 | Ap | Aq
B1 | Bp | Bq | B2
Cp | Cq | C1 | C2
Dq | D1 | D2 | Dp
| => | striping must be specified in the following way:
0 1 -1 -2
2 -1 -2 3
-1 -2 4 5
-2 6 7 -1

JBOD/Spanned. Just a bound of disks which are used as one continuous disk. There is no data alternation, stripe size is not used. Data located on any disk will be lost if the disk is absent. JBOD is supported in read/write mode.

### RAID parameters

Stripe Size: data rotation block size. Not used in RAID-1, JBOD
Delay: used in RAID-5 and RAID-6 with delayed parity only.
Offset: data start offset on disk (usually used on software RAIDs).
Offset and Size: partition offset and size for JBOD/Spanned disks.
Null disk: used instead of absent or damaged disk.
Striping...: manually specify striping for Custom RAID.
Save/Load: save/load RAID configuration.