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Here is the situation: I had a full backup, and a differential backup. I have restored the full backup into the database. But accidentally lost that backup file.

Now I would like to apply the differential backup. Normally you must restore from both the full backup, and the differential, without opening the DB for use. However, we have opened the DB, but not made any updates.

We have made a NEW full backup, which should be identical the the original full backup, except for at least the timestamp. That is, SQL Server detects that the differential is not taken from exactly that DB with that full backup.

Is there any way to trick SQL Server into allowing a differential to work with with new full backup? (I realize it is risky, but the data is important and willing to risk some errors.)

Is there any other way to get the updates out of the differential backup so they could be applied manually? Is there any "decoder" for a differential backup file? Any special recovery tools for this kind of situation?

  • If the LSN (Log Sequence Number) has not changed, then you should be able to take a new backup of the database that is live. After doing that you can then Restore with NoRecovery and then Restore the Differential with recovery. I think that will get you what you need anyway. – mskinner Aug 25 '15 at 2:21
  • As a side note, since you have concerns I would certainly recommend not restoring it to the same environment but trying it on a test environment first, just in case there were some changes made that you were unaware of. – mskinner Aug 25 '15 at 2:36
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No, sorry. Once the log chain was broken the following differential cannot be restored because there are at least a few transactions that would be lost. You may feel that those 'unimportant' changes could just be ignored. But SQL Server insists on a complete restore chain.

Though there are certainly some companies that will try to reconstitute a database for you. Not for free, of course.

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