Are You Wasting Backup Time?
If your company has a computing policy that's at all responsible, you back up your data on a regular basis. That's just common sense.
But a little-known feature of Microsoft's Group Policy Objects (GPOs) may be making it harder for you to have a sensible backup program. Allow me to explain.
Three Basic Types of Backups
Corporate backup procedures come in an infinite variety, but the following three types are among the most well-known:
- Full backup – A complete copy of all files is made. The backup software clears or resets the "archive bit" that each file carries. If a file is modified at some point after a backup, the operating system turns the file's archive bit back on. This allows backup programs to select those files that have recently changed.
- Incremental backup – Since full backups can be very time-consuming, incremental backups can be scheduled. These copy only new and modified files: those that have the archive bit set "on." Software that performs an incremental backup then clears the archive bit, so the next incremental won't copy files unnecessarily.
For example, if you performed a full backup on a Sunday night, and incremental backups on Monday and Tuesday nights, a disk failure on Wednesday morning would require you to run a restore operation from the Sunday, Monday, and Tuesday night backup media.
- Differential backup – Because restoring from multiple backup media can be time-consuming, some companies use differential backups. These copy files that have the archive bit set "on," but do not clear the archive bit. Every time a differential is made, it copies every file that has been modified since the last full backup. A disk failure on a Wednesday morning, to use the example above, would require you to run a restore operation only from Sunday's full backup and Tuesday's differential.