ANSWER:

I see there being a very real chance of your IO speed showing down substantially. When an LVM snapshot is enabled, it can be much slower. See the results found here when comparing: http://www.nikhef.nl/~dennisvd/lvmcrap.html

I think that is reason enough to avoid this method, but even so, there are other issues with snapshots that you should be aware of. The size of the snapshot cannot be exceeded, if this happens, the kernel will drop your snapshot. In this case, I would expect that to crash your virtual machine.

by GoldenNewby from http://serverfault.com/questions/381868