I am curious to find in my environment how much worse a file based VM is at file access vs one that is based on a physical partition.

File based VMs are much easier to manage and backup, but at what cost?

From my “squeezecenter” VM which is file based, I got these numbers from bonnie++

Version 1.01d       ------Sequential Output------ --Sequential Input- --Random-
---------------------Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
squeezecenter 1040M 41968  36 125483  30 24902   4 81678  72 498510  21  1554   2

Version 1.01d       ------Sequential Output------ --Sequential Input- --Random-
---------------------Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
squeezecenter 1040M 47747  42 169474  40 24596   4 60837  55 495674  27  1565   3

Version 1.01d       ------Sequential Output------ --Sequential Input- --Random-
---------------------Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
squeezecenter 1040M 55959  48 106715  25 22513   3 97244  86 493393  15  1552   1

And now similar output from a VM (web-server02) based on a physical partition :

Version 1.01d       ------Sequential Output------ --Sequential Input- --Random-
---------------------Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
web-server02  2064M 27455  23 27893   5 11294   0 21575   3 22615   0 124.1   0

This flawed because this machine is actually running off a USB drive.