zfs error: cannot destroy : dataset is busy

I just ran into the same issue with multipath as mackpaul1967 confirmed. I am concerned this will have adverse affects on replication, migration and/or backups. I had just emailed "office@proxmox.com" about multipath support and was told it was supported but not much detail. It might be a show-stopper for me, so if anyone has extra information I would greatly appreciate it.
 
I know this is a little old now but for those still struggling with this I was able to replicate and solve without rebooting. Make sure the container you are trying to delete is not included in the current backups, if it is go to Datacenter > Backup > Select the Backup entry and click on Edit, un-check the box for the container you want to delete and click ok. I followed this process and was able to delete the zfs vol without issues.
This worked for me, thank you. There was an orphan dataset for the CT# on the target node I was trying to replicate to (maybe a removed CT that never got cleaned up) and I couldn't remove it because it was "busy". Removed it from the backup jobs on the cluster and I could remove the dataset with the -r option to remove children as well. Then I could initiate the replication from the original node to the target, and add the CT back to the backup job for the cluster.
 
I have had the similar situation on test server with undestroyable "vm-137-disk-2" that was not mount, without any snapshots and VM 137 did not exist from long ago:

>zfs destroy -r -f rpool/data/vm-137-disk-2
cannot destroy 'rpool/data/vm-137-disk-2': dataset is busy

I have fixed this with following procedure:
>fuser -am /dev/rpool/data/vm-137-disk-2
/dev/zd64: 2633

PID 2633 was KVM
I have stopped all KVM VMs and after that I'll be able to destroy vm-137-disk-2 even from Proxmox GUI.
Thank you!! Filebrowser add-on from community scripts was the culprit.
 
Thank you!! Filebrowser add-on from community scripts was the culprit.
@OneMeanRabbit - Thank you - after hours of searching and trying to release what was holding onto my ZFS disk for a LCX I was trying to remove, your comment on Filebrowser being the cause was exactly the fix. Had installed via community script, stopping the Filebrowser service then let me immediately remove the lxc container and the zfs error was gone. Amazing!!