tavshed

Create a new Xen instance yesterday and had issues getting it started. Already have 4 instances running and the error message “Failed to find an unused loop device” kept appearing.

I could shutdown another instance and bring the new one up, but then the instance I had shutdown would not come back up and had the same error.

Luckily, I ran across the following post that provided all the information.
http://denraelevisgniht.blogspot.com/2011/01/failed-to-find-unused-loop-device.html

I created file /etc/modprobe.d/local-loop with one line.
options loop max_loop=64

After reboot, all instances would come up without a problem.