For the record, I had around 170 000 snapshots when I started.
I am currently trying to reduce it by running variations of this oneliner to get rid of them, to allow zfSnap -d to work again. for v in $(zfs list -t snapshot zfstank/volume | \ awk '/2019.*--5d/ {print $1}'); do zfs destroy $v; done -- Happy hacking Petter Reinholdtsen