Differential Partition Backup and Disk Defragmentation: Self-Defeating?

I own Hard Disk Manager 2009 Pro and Backup & Recovery 10 Suite. I have never used the Differential Partition Backup feature as I always create Full Partition images (and always from the WinPE CD).

However, I am interested in the Differential Partition Backup, but I wanted to know whether disk defragmentation will cause the program to duplicate sectors which have simply moved due to disk defragmentation. I use Norton 360 v3, which performs disk defragmentation in the background during idle times. Will the program recognize that sectors have simply moved and not back them up again?

Also, the last step mentioned on the status screen is "Merge Differential Backup." What is this? I should think the idea is to keep them separate.

 

Hello Michel Dufrenoy,

Defragmentation will affect differential backups in the sense that, the program will think data has been moved and backs up redundantly. For instance, in your base image, a file was backed up from sector address X, after the defrag, if the file has been moved to sector address Y, the differential backup will process the file has if it's a new file. There's going to be a redundancy of the files moved, one existing in the base image, and the other in the differential.

Merge differential backup is when you want to consolidate differential backups to eliminate redundancy.

For instance:

Differential Backup 1 has files A, B, C, X
Differential Backup 2 has files A, B, C, Y

The Merged Differential Backup will have files A, B, C, X, Y - saving you space of files A, B, C. This of course assumes you don't need to restore files X without Y, or vice versa.

Finally, to take one step further, the "Synthetic Backup" will consolidate a differential backup and a base backup to form an updated base image.

 

Gee...shouldn't there be a warning or other highlight in the help doc (aka "manual") that defrags can seriously effect the utility of differential backups? I ran across this same issue, and it was only my extensive systems background that suggested this would probably an issue; hence I found this thread. Thanks for confirming it, Tommy.