@alejandro-anv I have had problems like this on my NFS and iSCSI SR's previously.

One thing that might help is to shutdown the VM's before doing a re-scan. If my memory serves me, it does a different kind of coalesce (online vrs offline) and this has a better chance of success.

Also, be aware that from the time you re-scan and the time it actually starts to do work on the drives is 5 minutes.

When I have a problem like this, I normally ssh into the pool master and tail the logfiles to watch it work. IE:

tail -f /var/log/SMlog | grep SMGC

Its boring.. But.. it gives me a bit of comfort between prayers 8-)