Mirror overwritten with old data - can it be recovered?

Posted on 2006-06-08
Last Modified: 2010-04-03
Ok, situation is this:

Server has two scsi drives which are mirrored.
Disk management shows disk0 (master of mirror set) as missing. We believe this has been the case for about one month. When the master of a mirror set goes offline my understanding is that the server would have rebooted at that point and the server would have rebooted to the slave.

Anyway, the server was shut down for general mtce and when it restarted disk0 came back online and my limited understanding of mirroring tells me that it then reinstated itself as the master of the mirror set and started to resynchronise with the slave.

The problem now is that the data on the master was about one month old and has overwritten the data on the slave which was current. I don't understand exactly how the data is copied or synchronised between the master and slave in a mirror set so my question is this: I am trying to recover the missing data using R-Studio, do I have any hope in recovering the lost data or am I wasting my time?
Question by:barnesm6
    LVL 10

    Expert Comment

    The more full the hard drive is, the less you will be able to recover. If the old data overwrote the new data, then that new data is pretty much unrecoverable. If the new data was not overwritten, then it may be possible to recover the files that was sitting on those unwritten sectors.
    LVL 87

    Expert Comment

    Restoring a backup is much less a waste of time and will work if the backup was good. Trying to recover like you are is most likely futile, although you might get some data recovered. It probably won't be all, and you won't be sure if you are restoring the correct version of a file, there may several versions of the same file around!
    LVL 9

    Accepted Solution

    The entire disk will have been overwritten when the mirror rebuilt even if there was hardly any data on it so you are out of luck. The only way to recover the data now it through very specialised equipment that can read what was there before it was overwritten by subtracting the data from itself and seeing the faint signal of previous data. Only very specialised electronics can do this an it will cost thousands.
    LVL 1

    Author Comment

    I understand that recovering from a backup is easier so I probably should have mentioned that the last full backup is just as old as the data from the mirror.

    David is spot on with his reply. I've already spoken to a specialist data recovery company and they have explained that when a mirro synchronises the data is copied sector for sector so new files on the one drive will have been overwritten with empty space.

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