XEN with loopback devices
One of the most annoying things with XEN and loopback devices is that at some point you will run out of them. Especially if you like me have a setup with more than 15 virtual servers (not all of them are running at the same time).
I just ran into “Error: Device 5632 (vdb) coulnt not be connected. losetup $lo flags $loopdev $file”, which after some digging means that there are no free loopback devices.
The nice thing is that there is a way to solve it, instead of having;
In your DomU replace
disk=[ ..., 'file:/..../file.iso...
with
disk=[ ..., 'tap:aio:/..../file.iso...
Then you DomU should start just fine.
Read more here.