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Archive bit set during full backup

rhkay
Level 2

Does the archive bit for full backups get set when the job begins or when it successfully completes?  We have some weekly fulls that are failing because they are overrunning the tape, but the daily differentials are working fine.  What I want to know about the differentials is - are they differential from the last successful full or from the last attempted full?  Thanks.

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pkh
Moderator
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A full backup would backup every file in the selection regardless of whether the archive bit is on or off.  A differential backup only backs up files with the archive bit on.  For both types of backups, the archive bit is reset when the file is backed up.

Suppose your full backup is to back up 100 files and file no. 10, 20, 30, 40, ,, 90, 100 have the archive bits on.  Let's say, the full backup job fails after backing up file no 50, it would contain files 1 - 50.

Files 10, 20, 30, 40, 50 will now have their archive bit reset, i.e. off.  Files 60, 70, 80, 90, 100 will still have their archive bits on.

There are some changes to files 5, 15, 25, so their archive bits are turned on.

When you do your differential backup, it will backup files 5, 15, 25, 60, 70, 80, 90, 100 because only these files have their archive bit on.  Files 51 - 59, 61 - 69, 71 - 79, 81 - 89, 91 - 99 will not be in either your full (because it failed) or in your incremental backup.

This is why it is important to repeat your full backups if they failed because they are the baseline backups.

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pkh
Moderator
Moderator
   VIP    Certified

A full backup would backup every file in the selection regardless of whether the archive bit is on or off.  A differential backup only backs up files with the archive bit on.  For both types of backups, the archive bit is reset when the file is backed up.

Suppose your full backup is to back up 100 files and file no. 10, 20, 30, 40, ,, 90, 100 have the archive bits on.  Let's say, the full backup job fails after backing up file no 50, it would contain files 1 - 50.

Files 10, 20, 30, 40, 50 will now have their archive bit reset, i.e. off.  Files 60, 70, 80, 90, 100 will still have their archive bits on.

There are some changes to files 5, 15, 25, so their archive bits are turned on.

When you do your differential backup, it will backup files 5, 15, 25, 60, 70, 80, 90, 100 because only these files have their archive bit on.  Files 51 - 59, 61 - 69, 71 - 79, 81 - 89, 91 - 99 will not be in either your full (because it failed) or in your incremental backup.

This is why it is important to repeat your full backups if they failed because they are the baseline backups.

rhkay
Level 2

Thanks. That gives me the information I needed.