Last week I tried to use two virtual servers (based on Virtuozzo) to learn something about DRBD. As DRBD syncs a block debice I wanted to set up a loopback device and sync that across both servers.
Unfortunately all my tries to get the loopback device to work resulted in an error “no permission to look at /dev/loop#”.
Today I found the solution in the OpenVZ forum: there is no support for loopback devices in machines running on OpenVZ/Virtuozzo.