Pinal Dave at SQLAuthority.com posted an interesting question that tested my knowledge. I was sure there was a way to complete his question, but I haven’t had much experience with databases in FULL recovery model in the past.
Let us assume that you have corrupted (beyond repairable) or missing MDF. Along with that you have full backup of the database at TimeA. Additionally there has been no backup since TimeA. You have now recovered log file at TimeB. How to get the Database back online with the same state as TimeB?
My response is as follows.
On a test system, I created a database FullBackupTest with Full Recovery Model.
I created a table TableA.
I inserted a single record into TableA.
I took a full backup of FullBackupTest.
I stopped SQL Server Service and copied both the .mdf and .ldf files to different folder.
I started SQL Server Service
I inserted two more records into TableA.
I then stopped the SQL Server Service.
I then deleted the .mdf file in the Data directory.
I started SQL Server.
Database FullBackupTest failed to come online.
Just for tests, I stopped SQL Server Service again and copied the .mdf file back from the copy I made manually (I now have the .mdf file from an earlier copy out of sync with the .ldf file).
I started SQL Server and the database failed to come online.The Error in the log file was
2011-04-14 21:13:15.37 spid16s Error: 5173, Severity: 16, State: 1.
2011-04-14 21:13:15.37 spid16s One or more files do not match the primary file of the database. If you are attempting to attach a database, retry the operation with the correct files. If this is an existing database, the file may be corrupted and should be restored from a backup.
Looks good, can’t just do that, as I expected. For further testing, I did the following
I switched FullBackupTest to Emergency Mode
I switched FullBackupTest to Single User Mode
I ran dbcc checkdb (FullBackupTest).
No errors were reported.
Database would not switch from Emergency to Online mode with same error as above.
I then ran dbcc checkdb (FullBackupTest, repair_allow_data_loss)
Database would then switch to Online mode, however we were back to a single record in TableA, so it was just the same as a restore from the full backup at TimeA.
Then I stopped SQL Server Service one more time, and restored both the mdf and ldf from the manual copy.
Started SQL Server, verified FullBackupTest came online, and there were three rows in TableA.
Stopped SQL Server Service
Deleted the .mdf file
Started SQL Server Service.
FullBackupTest failed to come online again.
In Management Studio I executed
BACKUP LOG FullBackupTest TO DISK='FullBackupTest.trn' WITH NO_TRUNCATE"
RESTORE DATABASE FullBackupTest FROM DISK='FullBackupTestTimeA.bak' WITH NORECOVERY
This set the database in RECOVERING Mode and allowed me to restore Log File Backups.
I then executed
RESTORE LOG FullBackupTest FROM DISK='FullBackupTest.trn' WITH RECOVERY
Once complete, I find three rows in TableA as I expected to.
The keys are
1) To make sure you backup the tail of the log on the lost database.
2) Restore the full backup using the WITH NORECOVERY
3) Restore the log file backup from Step 1 using WITH RECOVERY to switch back to Online mode.
Great question Pinal!