RAID and spanned volumes

Use this dialog to reconstruct a broken RAID or spanned volume. Do not use it if the volume is not broken even if it has been reformatted or become corrupted. For more information please read:

What is a broken RAID?

Recover software RAIDs.

Recover hardware RAIDs.

Recover NAS devices.

RAID and NAS analysis services.

Volume type

Select a volume type (RAID 0, RAID 5, RAIDZ1, Spanned volume, ...).

Number of disks

Enter number of disks in the original volume. For RAID 0 or spanned volume all original disks must be available. For RAID 5 or RAIDZ1, one disk can be missing. For RAID 6 or RAIDZ2, two disks can be missing. The missing disk(s) must be included in this count.

Parity rotation

Parity rotation is only applicable to RAID 5 and RAID 6.

Warning: This section provides general guidelines. The parity rotation used by a particular manufacturer is subject to change without notice.

Backward symmetric

The parity block is rotated from the last disk to the first disk. The data blocks in a stripe start after the parity block and wrap around. If the parity block is on the last disk, stripe data starts on the first disk. Select this option if a software-based RAID 5 was originally created on a computer running Windows Server 2000 or later. Many new hardware RAID controllers also adopt this rotation scheme to equally balance the loads on all disks.

Backward asymmetric

The parity block is rotated from the last disk to the first disk. The data blocks in a stripe start on the first disk (or second if the parity block is on the first disk).  This has been observed on the Dell MegaRAID®, HP (formerly Compaq) controllers and many new controllers. (Please read the warning above.)

Forward symmetric

Similar to Backward symmetric, but the parity block is rotated from the first disk to the last disk.

Forward asymmetric

Similar to Backward asymmetric, but the parity block is rotated from the first disk to the last disk.

The next two rotations are only applicable to RAID 6.

Backward symmetric, shift 2

Similar to Backward symmetric, but the P and Q parity blocks are shifted two columns on each rotation.

Backward asymmetric, shift 2

Similar to Backward asymmetric, but the P and Q parity blocks are shifted two columns on each rotation.

Block size

On RAID volumes, data is written in stripes across all disks. You need to supply the size of a block in a stripe. Software-based RAIDs always use a block size of 64 kilobytes. Hardware-based RAIDs usually use 64 kilobytes as the default size unless a different size was chosen during initial RAID setup. If the block size is not known, you may want to consider our RAID analysis service.

Parity delay

This value should be 16 for the HP (formerly Compaq) RAID controllers and 1 for others. 3Ware controllers may use parity delay 8.