There's some very good plugins for reporting with PFSense 1.2. Have a look in the packages. Darkstat is useful for overall traffic patterns, and ntop is useful for breakdowns (which may be what you are after). bandwidthd has a god-ugly interface, but it can give some very useful long-term statistics.
Unfortuantely I'm not in an office that's got a pfsense box in it at the moment, so my memory can't be any clearer.
I suspect you are probably running into the issue that I'm going to call the "512 byte sectors are not 4K sectors" issue. Anyway, google up on gnop, 4K sector, WD Green and I suspect you'll find the fix. I first learned of it on this site, and it was very informative about that issue, as well as a variety of other tunings for FreeBSD and ZFS. Good luck!
Edit: to quote from the linked site:
... Finally, I came across references to
problems with Western Digital’s 1.5 TB
(WE15EADS) Green drives that I am
using.
The drives have a 4KB physical sector
but report 512 Bytes to the BIOS. So
performance drops off on really big
writes because zfs on FreeBSD sends
4KB of data to the drive as 8 separate
writes of 512 bytes, which requires
the firmware in the drive to increase
its work load by an estimated factor
of 60 (1st 512 Bytes - write 4KB, 2nd
512 Bytes, read 4K, write 4K, ..., 8th
512 Bytes, read 4K, write 4K -- so 4KB
of writes become 4KB write + (4KB read
+ 4KB write)X(4KB/512Bytes - 1) = 60. The drives built in 32 MB cache helps
until it fills and the zfs arc kicks
in and then the arc begins to fill.
So all in all, no big deal right?
Actually it is a very big deal if you
are writing files to zfs that are
larger than your arc plus the size of
the buffer on the drive. ...
Best Answer
pfSense 2.0, currently at RC1, has a 64-bit (AMD64) build. See their official FAQ.