SQL Server Backup and Restore - Simple Talk

Chapter 1: Basics of Backup and Restore
for databases that are simply too large to back up in a single operation. However, they are
not required on every database you manage. Unless you have experience with them, or
know definitively that you will gain significant performance with their use, then sticking
to a single data file database will work for you most of the time (with the data being
automatically striped across physical storage, via RAID).
Finally, before we move on, it's important to note that SQL Server transaction log files
are never members of a filegroup. Log files are always managed separately from the SQL
Server data files.
Transaction log
A transaction log file contains a historical account of all the actions that have been
performed on your database. All databases have a transaction log file, which is created
automatically, along with the data files, on creation of the database and is conventionally
denoted with the LDF extension. It is possible to have multiple log files per database
but only one is required. Unlike data files, where writes occur in a random fashion, SQL
Server always writes to the transaction log file sequentially, never in parallel. This means
that it will only ever write to one log file at a time, and having more than one file will
not boost write-throughput or speed. In fact, having more multiple files could result in
performance degradation, if each file is not correctly sized or differs in size and growth
settings from the others.
Some inexperienced DBAs don't fully appreciate the importance of the transaction log
file, both to their backup and recovery plan and to the general day-to-day operation of
SQL Server, so it's worth taking a little time out to understand how SQL Server uses the
transaction log (and it's a topic we'll revisit in more detail in Chapter 5, Log Backups).
Whenever a modification is made to a database object (via Data Definition Language,
DDL), or the data it contains (Data Manipulation Language, DML), the details of the
change are recorded as a log record in the transaction log. Each log record contains
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