Options for Backup Strategies

A Backup Article Contributed by Andrew Whitehead

The Ever Shrinking Backup Window

A backup window is the time it takes to complete a given backup, and is determined by both the quantity of data to be backed up and the speed of the equipment. As the time it takes to perform the backup grows with amount of data, backups can easily encroach onto production time, especially as many organizations run 24 hours a day leaving very restricted or even nonexistent backup windows.

Backup Alternatives

If you have the time to perform them Full Backups are the ultimate. A single tape, or set of tapes, can provides the means of returning a server to its present state. They do have drawbacks, the main one being security. If a full backup tape is stolen, the thief has an entire copy of your data.

In an incremental backup, only files that have changed since the last backup are included, making it much quicker than a full backup. The disadvantage is restore time. Restoring from an incremental backup requires the most recent full backup as well as every incremental backup since the last full backup. Imagine that you did a full backup on Friday, followed by incremental backups on Monday, Tuesday, and Wednesday, and your server crashed Thursday. To restore your system you would need the full backup tape from Friday plus the incremental backup tapes from Monday, Tuesday, and Wednesday.

Differential backups offer a compromise by backing up files that have changed since the last full backup. Restoring is easier as only two tapes are needed - the last full backup and the latest differential.

If the backup window is too small for the other options, synthetic full backups can be used. Information, taken from a full backup and a differential or incremental is used to create a new full backup tape offline.

Backup by File System Snapshots

A file system snapshot is an instantaneous image of a file system, and offers the ability to create reliable backups without shutting down running applications for fear of changing while the backup is being made. Snapshots have several important features, including the ability to make backups of the file system several times a day without needing large amounts of additional storage media, they are a convenient method of making file system integrity checks on a running file system, and most importantly create reliable off media backups without the need for inconveniently long backup windows.

Using Volume Shadow Copy Technology in Windows Server 2003

Volume Shadow Copy Technology(VSCT), introduced with Windows Server 2003, is Windows own snapshot technology. VSCT has three main features; open files are no longer left out, applications can continue writing to the volume during backup, and backups can be made at any time without worrying about the backup window or locking out users.

VSCT achieves this by creating shadow copy backups of volumes. These are exact instantaneous copies of files, and include all the open files. This means that files opened by operator or system activity, or databases that are continually held open, are backed up during a volume shadow copy backup.