SQL Server Backup and Restore - Simple Talk

Chapter 9: File and Filegroup Backup and Restore
We can see that the first three RESTORE commands executed successfully but the fourth
failed, with a message stating that the LSN contained in the backup was too recent to
apply. Whenever you see this sort of message, it means that a file is missing from your
restore script. In this case, we forgot to apply the differential file backup for the secondary
data file; SQL Server detects the gap in the LSN chain and aborts the RESTORE command,
leaving the database in a restoring state.
The course of action depends on the exact situation. If the differential backup file
is available and you simply forgot to include it, then restore this differential backup,
followed by TLOG2, to recover the database. If the differential file backup really is missing
or corrupted, then you'll need to process all transaction log backups taken after the full
file backup was created. In our simple example this just means TLOG and TLOG2, but in a
real-world scenario this could be quite a lot of log backups.
Again, hopefully this hammers home the point that it is a good idea to have more than
one set of files on hand, or available from offsite storage, which could be used to bring
your database back online in the event of a disaster. You never want to be in the situation
where you have to lose more data than is necessary, or are not be able to restore at all.
Summary
In my experience, the need for file backup and restore has tended to be relatively rare,
among the databases that I manage. The flipside to that is that the databases that do need
them tend to be VLDBs supporting high visibility projects, and all DBAs need to make
sure that they are well-versed in taking, as well as restoring databases from, the variety of
file backups.
File backup and restore adds considerable complexity to our disaster recovery strategy, in
terms of both the number and the type of backup file that must be managed. To gain full
benefit from file backup and restores, the DBA needs to give considerable thought to the
file and filegroup architecture for that database, and plan the backup and restore process
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