Klennet Storage Software

Analyzing block map in RAID0

This is an example of block map and disk order analysis in a RAID0. The disk set contains four drives from the RAID0 plus one extra drive unrelated to the array. The RAID block size and start sector were already determined in the previous episode.

1. Default view

The screenshot below is what I had once I switched from start sector and block size view to block map view. This looks mildly complex, but repeating pattern is clearly visible already. Let's see what we can find from here.

RAID0 initial block view.

Initial block view for a RAID0 sample.

First of all, the leftmost drive (labeled Disk2, near the top of the window) is not related to the RAID. This is a typical behaviour of a drive which is either not related to the RAID or is blank (often a hotspare). This drive is to be ignored. I prefer to exclude it from the display, by removing the checkmark under the drive name, but that's optional. Excluded drives are conspicously marked, as seen on the screenshot below.

2. Reordering

With the extra drive out of the way, let's sort four RAID drives.

Reordering of member disks in a RAID0.

Reordering disks in a RAID0 sample.

In each row of a RAID0 with N drives, there are N-1 transitions to the next block in the same row, and one transition to the next row. This latter transition is the key to RAID0 ordering. It always goes from the last block in a row to the first block in the next row. So, the ordering process for the RAID0 is as follows:

  1. Identify the transition between rows. You are looking for an arrow which
    • goes from one row to the next row and
    • repeats on each row.
    I have circled starting and ending point in the screenshot above.
  2. Arrange the drives so that the arrow goes from the last drive in the upper row to the first drive in the lower row. This is done by using drive ordering arrow buttons at the top of the screen.
  3. After the transition between rows is arranged, arrange remaining drives so that all the other arrows form a chain from the first to the last drive.

3. Final result

After reordering, we arrive at a very orderly map shown on the screenshot below. The correct RAID block maps have sort of an orderly, symmetric look to them.

RAID0 final block view.

Final block view for a RAID0 sample.

From here, we can read the correct disk order easily, which is Disk 4, Disk 3, Disk 5, Disk 6.

And this completes the analysis for this case. You can then put in this disk order and also block size and starting offset into whatever data recovery software you use.

Continue to a simple RAID5 example

Created Tuesday, October 2, 2018

I have a low volume mailing list, for news and tips, which I send out once or twice a month.
Subscribe if you are interested.