Differential Backup Confusion

cbriant

Hi,

I understand that Differential backups backup the data since the last normal backup, but what if a normal backup is performed, followed by an incremental and then a differential. Would the differential backup include all data changed since the normal backup or the incremental?

From what I understand normal and incremental backups set the archive bit whereas a differental leaves it. If the incremental backup has set the archive bit then wouldn't a differental backup record all files which don't have the archive bet set which is effectively recording all files since the last incremental backup?

I just need to be clear on this before taking the exam in case they catch me out.

Sie

Check this out:

http://www.techexams.net/technotes/xp/backup_restore_repair.shtml#backup

royal

Full Backup - Archive bit cleared
Diferential Backup - Archive bit not cleared
Incremental Backup - Archive bit cleared

Friday - Full Backup - All archive bits turned off
Monday - Differential Backup - Only files that have been modified since Friday (archive bits on those files turned on) will be backed up. Archive bit not modified
Tuesday - Differential - Files since the last full backup that have been modified which causes those file's archive bit to be turned on. Those files are backed up in addition to the files that were backed up on Monday. The files that were backed up on Monday are still backed up because Monday's Differential backup left the archive bit turned on.
Wednesday - Incremental - All modified files that have been modified since the last full backup are backed up since the differential backup left the archive bits turned on. This incremental backup turned off all the archive bits.
Thursday - Differential - All modified files since Wednesday are backed up, and only since Wednesday. This is because the incremental backup from Wednesday turned off the archive bits for the files that have been modified since the last full backup.

Normal Backup is a full backup but doesn't turn off the archive bits. Basically, you use this when you need a full backup but don't want to mess with your backup strategy.

Daily backup is a backup of only files that have been modified the same day the daily backup is being run. The archive bits are not modified. Just like a normal backup, you use this when you don't want to mess with your backup strategy.

Does this help?

cbriant

Thanks for the example, this is how I thought it was I just had the archive bit detail muddled up.