I get this error when backing up a vm, it gets to 25% and fails "job failed with err -61 - No data available" I can't find anything on it in the forums.
Hi,
that most likely means there is an issue with the underlying storage/disk. There are quite a few threads with that message, e.g. this one. You can use something like https://www.gnu.org/software/ddrescue/ to salvage the parts of the disk that can still be read successfully.