Xen image file vs partition/LVM volume performance

I read quite a lot of advice to switch from file-image VM storage, to partition/LVM volume based.

The claim is that partition/LVM are much faster then image files.

The downside in my opinion, is that one no longer have the whole VM in a single, easy to copy and migrate file.

Can anyone advice on this, especially if there indeed any difference in new versions of Xen, and if there are any IO benchmarks to support it?

Thanks!

Solution 1:

Creating a block level access to virtual machine state, as opposed to a file level access will always be faster because there is a layer of abstraction removed.

I would recommend the LVM approach. Don't forget, you can always backup the LVM volume just like a file. There isn't much difference between the two. LVM is also quite flexible in terms of relocating the data.

Just because the abstract notion of a file doesn't exist anymore doesn't mean it is bad. The performance gains may be considerable, and with a little bit of broad thinking you can plumb your infrastructure just like it was a file.

I often make a partition for QEmu virtual machines. Then I can use dd to save and restore it. One file system (the virtual machines) running down to block level is better than a file in a filesystem with a filesystem atop.

Good luck

Solution 2:

I'll just add to all the answers above, by reminding you that LVM has a somewhat easy to use snapshot mechanism. This makes it pretty easy to backup or clone running VM's by simply making a snapshot, cloning or backing the VM up, and removing the snapshot. All without downtime.