On 03/09/17 21:23, Russell Coker via luv-main wrote:
It turned out to be BTRFS mis-managing free space,
deciding there was
none left, and going into read-only mode. The QEMU/KVM server blocked
on disk IO and paused the virtual machines, which meant that they
couldn't even respond to pings.
I've setup a cron job to run a weekly balance on the BTRFS filesystem
which will prevent this happening again. I've seen similar things in
the past but didn't expect them in this case because the filesystem is
only 50% full.
Ouch! Well worth knowing about that risk. Thanks again, Russell!