Bad rawio/raid performance

[David Teigland]

Has anyone else tried raw-io with md devices?  It works for me but the
performance is quite bad.  

Using raid0 across 4 disks I get about 40 MB/sec from /dev/md0.  After a
"raw /dev/raw1 /dev/md0" I only get 2 to 3 MB/sec from /dev/raw1.  Going
back to md0 after this, throughput is wrecked and will only be 2 - 3
MB/sec from md0.

I recompiled with read-ahead set to 0, but it didn't help.  Any ideas?
I'm using the latest raid and rawio patches.

Thanks,
Dave Teigland