RAID 0 Recovery

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How to recover RAID 0 manually

RAID 0 recovery means the recovery of the array configuration. Usually that includes data order on the member disks and block size. You can recover these parameters either manually or automatically (using special RAID recovery tools).

How to determine block size

Block size can be specified either in sectors or in kilobytes. 1 KB = 2 sectors. You should be careful not to mix the units. The fastest and most reliable way to find out block size is to look up its value somewhere, for example:

• take some spare drives, create a new array, and notice the default value;
• look for the values in the web - there is always a chance that someone faced the same issue;
• search the member disks manually for the parts of some particular large file and analyze the location of its fragments (see below).

How to determine a data order on the member disks

To determine data order and confirm block size you need to:

• find a copy of any large enough file which was for sure stored on the array,
• have a tool to view disk content such as WinHex or ZAR data recovery software, The demo version of either will do.

Choosing the file for analysis

Try to recall some large enough file (several megabytes) that is for sure stored on the RAID (it can be an image, music, video and so on). If nothing comes to mind, you can always do a RAW recovery for one of the member disks and see what images are stored on it. Surely you will not see a full image but even with fragments it is possible to indentify the file.

Searching the member disks for the file fragments

Launch the disk viewer tool to look for the fragment of this file (typically start with the beginning of the file) on one of the member disks. It is desirable to check that much more than one instance of the file fragment is not brought up during the search (two copies are OK but ten are not). If too many of such instances are discovered you should look for some longer fragment of the file, or even another fragment, for example from the middle of the file.

Note that it takes about an hour to search a typical array and it is not unusual to spend a week to recover the array entirely.

Once you have located a fragment of the file on the drive, you should look for its continuation on another drive. To do this you need:

• Go to the next sector on the other drive and search there for the file continuation.
  • If you don't see the file fragment in there, continue searching on other disks (see below).
  • If there is file continuation on the same drive it means you can determine block size - just scan the file fragment continuation and detect where it ends. Now we know order of disks as well: the first part of the file is located on the last disk while the second part is on the first disk in the array.
    For a RAID consisting of two or three disks, the disk order is determined completely. In case of more than three disks you need to search the member disks for the transitions between the file fragments.
• On the other disk go to the last analyzed sector minus supposed block size and search there for the file continuation. The typical values of block size are 32, 64, 128, 256, 512, or 1024 sectors.
  • If you have discovered the file continuation in there, you know block size and disk order. The disk holding the first part of the file is the previous to the disk storing the second fragment part. This data is enough to restore the configuration for the array of two member disks. If the array has more than two disks you need to continue with the search.
  • If nothing is found, you should try another block size.

Notes

1. If possible, pick large enough file for the fragment search.
2. The fragmentation complicates the work but typically the probability to come across a fragmented part of the file is less than 1%. Nevertheless, you can check a couple of files just in case.
3. If NTFS compression was used, the file data on the drive will differ from the original file content. This of course makes it difficult to analyze the array in such a way.