Tuesday, 5 October 2010

Imaging RAIDs

If you recover RAID and need to create a RAID image file, you should create the image files of the member disks rather than the whole array. Generally, it is not possible to restore the original array state using a RAID image file.

As for RAID0, the original state can be restored by writing the image to the array provided that the controller's settings (and thus the array parameters) have not been changed. If the controller's settings have been changed between reading and writing the image file, then image file data doesn't go to the original place on the member disks.

For RAID5 it is not enough to have a RAID image file of the entire array even if the controller's settings have not been changed. This is because the parity data is not written to the image file. If the array works properly, the parity data is not used, but for the RAID recovery you need the parity data. A RAID5 consisting of 3x1TB disks contains 3TB of raw data (with parity), while the array image file will be 2TB in size and, obviously, does not contain all the data.

The image file of the whole RAID, which was copied using an incorrectly configured controller, is a mess of the block parts and it can only be used provided that you know what the controller's settings were when creating the RAID image file. As of 2010, we know of no software capable of recovering such array image files.

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