Disk performance under CURRENT

I just ran test of disk writing performance under V4 (STABLE) and V5
(CURRENT) and was surprised at the difference.

The test was simple and not at all rigorous. Just a dd bs=256k
if=/dev/zero of=/dev/ad2. This is about the simplest way of dealing with
a disk. No file system or anything else. Just raw data to the device.

Under STABLE, I get an average of 25 MB/sec to the disk. Under CURRENT,
it drops to 15 MB/sec. I did this because I had noted that it was now
taking over an hour to backup my system disk (40 GB) when it was only
taking 40 minutes when I was running V4.6. The STABLE system was built
yesterday. The CURRENT system last Sunday.

Any idea why this is so much slower? It looks to me like it must be in
either geom or the disk driver.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman_at_es.net			Phone: +1 510 486-8634