Disk 100% busy

[Dan Nelson]

In the last episode (Oct 16), Will Saxon said:
> 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.

Are you swapping?  Check either "vmstat 1" or top output.  You can also
tell top to display blocking I/O requests per process by hitting "m",
then ask it to sort by I/O by hitting "ototal<enter>".

-- 
	Dan Nelson
	dnelson at allantgroup.com