Slow copy with little CPU/disk usage

A friend of mine has an application where he's copying in 4000 rows at a
time into a table that has about 4M rows. Each row is 40-50 bytes. This
is taking 25 seconds on a dual PIII-1GHz with 1G of RAM and a 2 disk
SATA mirror, running FBSD 4.10-stable. There's one index on the table.

What's really odd is that neither the CPU or the disk are being
hammered. The box appears to be pretty idle; the postgresql proces is
using 4-5% CPU.

I seem to recall others running into this before, but I can't remember
what the issue was and I can't find it in the archives.

This is version 8.0, btw.
--
Jim C. Nasby, Database Consultant decibel(at)decibel(dot)org
Give your computer some brain candy! www.distributed.net Team #1828

Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"