An efficient backup plan, authentically followed, is the foundation of any catastrophe improvement plan. A simple hard-drive failure can set a company back days or even weeks, without backups, as it tries to reconstruct lost data. One advantage of tape backup is that a user can run it unattended. The user can schedule tape backup to run automatically during off hours, when no one is using the network.



Every version of Windows comes with a built-in backup program. In addition, most tape drives come with backup programs that are often faster or more flexible than the standard Windows backup. Backup programs do more than just copying the data from the hard drive to tape. Backup programs use special compression techniques to squeeze the data in the compression ratio of 2:1. DAT (digital audio tape) units can back up as much as 40GB on a single tape, and DLT (digital linear tape) drives can store up to 80 GB on one tape.

Several backup schemes rely on full backups daily, but for some networks, it's more practical to use a scheme that relies on two or more of these backup types. The differences among the five types of backups involve a little technical detail known as the archive bit. The archive bit indicates whether a file has been modified since the last time it was backed up. A user can customize the file selection for a backup operation to suit the needs of the user. The drives and folders that a user selects for a backup operation are collectively called the backup selection.

A normal backup, also known as full backup, is the most basic type of backup. All files in the backup selection are backed up in a normal backup, regardless of the archive bit. In other words, the files are backed up even if they haven't been modified since the last time they were backed up. A daily backup backs up just those files that have been changed the same day that the backup is performed. A daily backup examines the modification date stored with each file's directory entry to determine whether a file should be backed up. Daily backups don't reset the archive bit.

An incremental backup backs up only those files that the user has customized since the last time the user had a backup. A differential backup is similar to an incremental backup, with the exception that it doesn't reset the archive bit as the files are backed up. The main difference between incremental and differential backups is that incremental backups result in smaller and faster backups, but differential backups are easier to restore. When back up of network data is taken, a user has two basic approaches to running the backup software- a local backup (software runs on the file server itself and backs up data to a tape drive that's installed in the server), or a user can opt for a network backup (network computer is used to back up data from another network computer).