??? Secondary data files: A database can also have one or more secondary data files
that have a default extension of .ndf. They are not required, nor do they hold any
file location data. Generally, you use secondary data files either to create storage
space on drive letters separate from the primary data file or to keep the size of each
individual data file at a practical maximum size, usually for portability.
??? Transaction logs: A database must have at least one transaction log file with a
default file extension of .ldf. The log is the lifeblood of the database??”without an
accessible transaction log, you can??™t make any changes to the database. For most
production databases, a proper backup scheme for a transaction log is critical.
When you make a change to the database, you do so in the context of a transaction:
one or more units of work that must succeed or fail as a whole. Transactions surround us
in our daily life. Simply going to the store to buy a pack of gum involves a transaction;
CHAPTER 2 n MAKING DATABASE BACKUPS 14
you give your money to the cashier, who in turn gives you the gum and your change.
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