[Beowulf] LVM performance problems

[Judd Tracy]

I am trying to bring up a small file server and am noticing some serious 
performance issues when using LVM.  I created a software raid /dev/md0 
which I can read at ~195MB/s using the raw raid device, but as soon as I 
put LVM on top of it the read speeds drop to ~95MB/s using a raw lvm 
partition without a filesystem.  When I use and xfs filesystem on top of 
the lvm partition it drops down to ~40MB/s.  This seems like a 
processing power issue, but the machine is a dual processor opteron 
system with 4GB of ram in it.  Does anyone have some insight into why I 
might be having such problems with the system.

Judd Tracy
Institute for Simulation and Training
University of Central Florida