Understanding Backup Types
Backup software can use or ignore the archive bit in determining which files to back up, and can either turn the archive bit off or leave it unchanged when the backup is complete. How the archive bit is used and manipulated determines what type of backup is done, as follows:
- Full backup
A full backup, which Microsoft calls a normal backup, backs up every selected file, regardless of the status of the archive bit. When the backup completes, the backup software turns off the archive bit for every file that was backed up. Note that “full” is a misnomer because a full backup backs up only the files you have selected, which may be as little as one directory or even a single file, so in that sense Microsoft’s terminology is actually more accurate. Given the choice, full backup is the method to use because all files are on one tape, which makes it much easier to retrieve files from tape when necessary. Relative to partial backups, full backups also increase redundancy because all files are on all tapes. That means that if one tape fails, you may still be able to retrieve a given file from another tape.
- Differential backup
A differential backup is a partial backup that copies a selected file to tape only if the archive bit for that file is turned on, indicating that it has changed since the last full backup. A differential backup leaves the archive bits unchanged on the files it copies. Accordingly, any differential backup set contains all files that have changed ...