Lost the zfs pools...

Today, I tried to copy a lot of files from a windows 10 machine to my zfs mirror raid.
After a couple of Gb The windows machine lost contact and when I try to connect to the share I get "Communication Failure" without any more info than that.

The bad part is that I also get Communication failure when I try and investigate the pool on the ZFS page.

I cannot even reboot the system from the GUI, so something is really bad.

What can I do to find more info on this? The log does not show anything odd.

After a hard reboot, the pools seems to work again.

But what can I do to prevent this from recurring? Not copy large folders from Windows, maybe. But that should not be a problem...