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View Full Version : Safe to delete earlier differential backups



Misty
24-08-2009, 09:56 PM
When you have done the original backup then have done a number of differential backups, is it then safe to delete some of the earlier differential backups leaving just the last one ? (Am talking particularly here of Acronis True Image).

I ask this because the differential backups for my photos take up 10 to 12 Gigs each. Deleting a few would save quite a bit of space. :illogical

However presumably having a number of sequential backups gives a greater degree of safety in that you can go back and chose an earlier differential if the last one is corrupted ? ie, similar situation to Windows system restore where you have a range of options.
Misty :waughh:

pctek
25-08-2009, 08:21 AM
It's not how I'd back up.

I'd use Acronis for the main Image and then just copy personal data to an external drive.

gary67
25-08-2009, 09:32 AM
I have set mine up to do a full backup once a week and a daily incremental each one gets over written in turn

Misty
25-08-2009, 07:38 PM
It's not how I'd back up.

I'd use Acronis for the main Image and then just copy personal data to an external drive.
Hi pctek
That's okay on my PC because the two operating systems and programs are on one HD and the the data on another. However on the laptop there is only one HD. I suppose I should partition the drive then it would be simple to just image just Windows XP Professional and programs :horrified - Then I could do as you do !

Misty

Misty
25-08-2009, 07:49 PM
I have set mine up to do a full backup once a week and a daily incremental each one gets over written in turn
Hi gary
I must get out my Acronis manual and have a read. :xmouth: You may be right, but I have always thought that each incremental was an addition, so that the second incremental was what had changed after the original backup plus the first incremental. Therefore nothing gets overwritten.

The differential always records the changes since the original backup, so that each succeeding differential supersedes the one before. That is why differential backups take longer than incremental backups.

I may stand to be corrected ;)
Misty

PS - of course you may be referring to a different program than Acronis :)

Blam
25-08-2009, 09:49 PM
Hi gary
I must get out my Acronis manual and have a read. :xmouth: You may be right, but I have always thought that each incremental was an addition, so that the second incremental was what had changed after the original backup plus the first incremental. Therefore nothing gets overwritten.

The differential always records the changes since the original backup, so that each succeeding differential supersedes the one before. That is why differential backups take longer than incremental backups.

I may stand to be corrected ;)
Misty

PS - of course you may be referring to a different program than Acronis :)

Incremental and Differential are the same in any program.;)

And from what I know, you are right too:)

WarNox
25-08-2009, 11:42 PM
Incremental and Differential differ in the way they deal with the 'archive bits' after a full backup is compleated.

Say you do a full backup on a Monday night. That full backup will remove the 'archive bit' on every file that it backs up.

If any one of those files is modified or if a new file is created during Tuesday the 'archive bit' will once again be set.

If on Tuesday night you do a differential/incremental they will back up exactly the same data. As they will only backup the files with the archive bit set. The difference is that the incremental backup will remove the archive bit when it backs up the file and the differential will not.

So on Wednesday the differential backup will once again back up everything that has changed since the full backup on Monday and the incremental will only back up what has changed since the last incremental backup.

To restore incremental = FULL BACKUP + INCT1 + INCT2 + ...
To restore differential = FULL BACKUP + THE_LAST_DIFF

Hope that makes sence, if not you can google it :)

---

To answer your question:

Yes you can delete the previous differential backups as long as you have the latest one since the last full backup. If you're worried about corruption that is another problem all together, depends on how safe you want to be.



Gregor

gary67
26-08-2009, 07:43 AM
I have Tuesday Acronis full backup, Wednesday incremental,same on Thursday and Friday, none at the weekend as I'm often away, Monday incremental. Tuesday the full overwrites last weeks full, Wednesday the new incremental overwrites last Wednesdays and so on. Therefore I only have One full and four incrementals on my backup drive for each computer on my home network