Protecting Data: Backup
A typical backup plan includes some combinations of these backup types performed at regular intervals. One common practice is to perform an incremental or differential backup each day and a full backup every week. Full backups make the restoration process easier because there is only one set of tapes; however, they also require a lengthy backup process each night, which often means that someone must physically change the tapes.
Incremental Backup
Incremental backups are much faster because they back up only those files that have been changed since the last backup. The Archive attribute switches on when a file is modified. An incremental backup backs up the file and then removes the attribute so that the file will not be backed up again unless it is changed the next day. A combination of incremental and full backups are usually results in four to six incremental tape sets and one full tape set each week. If the drive fails, the administrator must restore the last full backup set, as well as all the incrementals performed since the drive failure. This process obviously is considerably slower than a backup scheme in which a full backup is performed every night.
Differential Backup
Differential backups are similar to incrementals except that they do not reset the Archive attribute, which means that each backup during the week backs up all files changed since the last full backup. A full backup once a week (generally Friday or Saturday) and differentials every other day means that only two tapes will be needed in case of failure -- the last full backup and the last differential.
Keeping a log of all backups is important. Most backup utilities can generate a backup log. Microsoft recommends that you make two copies of the backup log -- store one with the backup tapes and keep one at the computer site. Always test your backup system before you trust it. Perform a sample backup, restore the data, and check the data to be sure it is identical to the original.
You can attach a tape drive directly to a single server, or you can back up several servers across the network at once. Backups over the network are convenient for the administrator, but they can produce considerable network traffic. You can reduce the effects of this extra traffic if you place the computer attached to the tape drive on an isolated network segment and connect it directly
Latest Articles