Bonnie++ results from running on one of the 250gig drives.

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
xen-steel 8G 71543 63 73234 14 33611 3 73275 65 78241 0 185.4 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 346 0 +++++ +++ 302 0 343 0 +++++ +++ 265 0
xen-steel,8G,71543,63,73234,14,33611,3,73275,65,78241,0,185.4,0,16,346,0,+++++,+++,302,0,343,0,+++++,+++,265,0

Bonnie++ results from running on the aufs mount.
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
xen-steel 11G 67460 60 57827 13 26490 5 57663 40 60691 2 186.2 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 372 0 +++++ +++ 294 0 363 0 +++++ +++ 220 0
xen-steel,11G,67460,60,57827,13,26490,5,57663,40,60691,2,186.2,0,16,372,0,+++++,+++,294,0,363,0,+++++,+++,220,0

Not much difference…