[Discuss] LVM vs File system file for KVM Virtual Machines?

[markw at mohawksoft.com (markw at mohawksoft.com)]

Hopefully without getting into an augment about the pros and cons of LVM
vs btrfs or zfs, does anyone want to discuss the pros and cons of LVM
"device" for a virtual machine vs a file on a file system for a virtual
machine?

So, do you create a 30G file on a file system, like EXT3, jfs, or xfs and
use that or do you create a 30G LVM device and use it directly? There are
some benefits to using LVM and with the 3.x kernel, you could even use a
"thin provisioned" device.

Which do you suspect would be more resource efficient? Which do you think
would have faster I/O?

I've set up two systems, one on a jfs file system and one on an "old
style" LVM partition. (Fully allocated). I don't see much of a difference.
I suspect the LVM based system should be more efficient because it does
not have to go through the intermediate file system layer to get to the
device layer. Internally, the VM sees the LVM device as its own device.