.trn is also the most common extension used to identify a log
backup. Every action against a database is assigned a Log Sequence Number (LSN). To
restore to a specific point in time, there must be a continuous record of LSNs. An uninterrupted
chain of log backups is absolutely critical for recovery purposes for databases in
Full or Bulk-Logged recovery mode.
CHAPTER 2 n MAKING DATABASE BACKUPS 28
Differential Backup
Restoring log backups tends to be a slow operation, especially if your full backup is a
week or more old. Differential backups are intended to decrease recovery time.
DIFFERENTIAL is actually an option for the BACKUP DATABASE statement:
BACKUP DATABASE Adventureworks TO DISK = 'D:\data\AW.dif' WITH DIFFERENTIAL,INIT
In this example, AW.dif contains all the changes made since the last full backup. You
can use it during the restore process in addition to transaction log backups. First, restore
the full backup, then restore the latest differential, then restore any transaction logs that
follow it.
Consider the following items when using differential backups:
??? If you perform full backups infrequently, differential backups will grow significantly
in size for an operational database: Remember, differential backups contain all
changes since the most recent full backup.
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