Disk 100% busy

[Will Saxon]

I am trying to diagnose a problem whereby a virus scanner (clam
antivirus) is taking too long to scan attachments on a mail server. We
have an attachment limitation of 20MB and an attachment of 7-20MB can
take over 3 minutes to scan. This often causes the sending mail server
to timeout and resend the mail.  

In this case, my mail gateway is is a dual 3.06GHz Xeon with 1GB of ram
and 2 36GB 15krpm drives in a raid-1 on a smart array 6i (cciss)
controller. I am running FreeBSD 5.4-RELEASE-p1. 

Systat -vmstat reports the disk mirror is 100% busy at all times on this
machine, with an average of around 300 tps at 15KB/t. This seems wrong
to me, as these numbers are maintained even when the system doesn't
otherwise appear busy. We don't seem to be swamped by log writes. How
can I tell what's generating these disk writes? At the moment the 100%
disk utilization is the only thing I can see that would cause the
scanning delay. The machine overall is sluggish with file operations. 

-Will

--
Will Saxon
Systems Programmer, Network Services
University of Florida Department of Housing
Phone: (352) 392-2171 x10148
Email: wills at housing.ufl.edu