Increasing loop devices on Xen host

by on May.18, 2011, under Linux, System Administration

Trying to start another Xen guest domain, and getting an error indicating that there are no loop devices left, like the following? :

Error: Device 51714 (vbd) could not be connected. Failed to find an unused loop device

Increase the number of loop devices that the loop kernel module will create, by editing/creating /etc/modprobe.d/local-loop containing something like:

options loop max_loop=512

Reboot, and you should be all good. (I did try to create new loop devices with mknod without rebooting, but that didn’t seem to work; I think the loop kernel module would need to be unloaded and reloaded at least – that requires stopping all guest VMs anyway, so at that point I decided I may as well just reboot.

(If you don’t have loop as a kernel module, but rather compiled into the kernel, you’ll need to modify your kernel’s boot line to include max_loop=x there instead.)

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