Linux bind / dhcp iowait status

[Tom Greaser]

have a beefy box that shows 18.40 % iowait at PEAK times
and as low as 5.50 % during work hours..

have 2000 phones lease set to 1 day

2000 pc lease set to 4 hours..

running ddns on this host ...

just wanting to see if this is "normal"

will track down to see if its named or dhcpd doing the bulk of IO wait..

Its an Redhat AS 4 update 3 box with mirrored scsi Ultra 320 drives
10000 rpm
bind-9.2.4-7
dhcp-3.0.1

from free -h 
buffer 137meg       cache 1627 meg

thanks for any echos