You know what, I would not bother.
Acronis does not deal well with media.
The only backup software I found that did was Retrospect. What it did was effectively checkpoint its backup stream at the beginning of each media and if it did not like the media after writing to it, it would say something like media failed insert new media 10 or what ever it was.
Acronis tries to treat the the media as a disk, on bad media you get the old retry/ignore/cancel message after backing 10 dvd’s. A really helpful flush the whole lot down the drain and start over approach.
I do not know what the quality of Retrospect is now I stopped using it some years ago.
Save yourself a lot of grief and backup to another harddisk.