No problem.
You might get an error saying not everything was backed up, and that's probably because a file existed when it inventoried the rootvg, then was gone when it was time to back it up. This tends to happen with monitoring software.
Something like this:
Creating information file (/image.data) for rootvg.
Creating list of files to back up..
Backing up 61472 files..............................
3142 of 61472 files (5%)..............................
5726 of 61472 files (9%)..............................
12440 of 61472 files (20%)..............................
16433 of 61472 files (26%)..............................
25074 of 61472 files (40%)..............................
43046 of 61472 files (70%)...................
0512-003 mksysb may not have been able to archive some files.
The messages displayed on the Standard Error contained additional
information.