SQL Server Backup and Restore - Simple Talk

Tail log backups
Chapter 1: Basics of Backup and Restore
In the event of a failure affecting a database operating in FULL or BULK_LOGGED
recovery model, the first action after the failure should be to perform what is known as
a tail log backup of the live transaction log, which captures the remaining contents
of this file. In fact, a subsequent RESTORE operation may otherwise fail, unless the
command includes WITH REPLACE, indicating that the existing database should be
overwritten, or WITH STOPAT, indicating that there is a specific point at which we wish
to stop the restore operation.
If a database is corrupted in some way, but is still online and we wish to restore over that
database, then performing a tail log backup with BACKUP LOG…WITH NORECOVERY, will
capture the remaining contents of the live log file and put the database into a restoring
state, so that no further transactions against that database will succeed, and we can begin
the restore operation.
This sort of tail log backup, as well as normal log backups, require the database to be
online (I believe, so that information regarding the log backup can be stamped into the
database header). If the database is offline, and an attempt to bring it back online fails,
perhaps because a data file is unavailable, then a tail log backup WITH NORECOVERY, as
well as any normal log backups, will fail. However, it may still be possible to perform a
tail log backup, but using the NO_TRUNCATE option instead, BACKUP LOG…WITH NO_
TRUNCATE. This operation backs up the log file without truncating it and doesn't require
the database to be online.
Of course, any sort of tail log backup will only be possible if the log file is still accessible
and undamaged but, assuming this is the case, it should be possible to restore right up
to the time of the last transaction committed and written to the log file, before the
failure occurred.
Finally, there is a special case where a tail log backup may not succeed, and that is if
there are any minimally logged transactions, recorded while a database was operating in
BULK_LOGGED recovery model, in the live transaction log, and a data file is unavailable
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