Before going out shopping for hardware, I'd try and determine where
your performance problem is, ie on the server (due to external USB
based storage), or on the client.
A good point, but either way I need a hardware upgrade. A single external hard drive isn't going to cut it. At the very least, I need redundancy for the pool. Regardless of any issues on the client, writing to the disk over USB will become a bottleneck with as much data as there is to back up. You're right, though, I can probably be pretty modest about any hardware upgrades.
It does seem to me that you are having a performance issue on the
system to be backed up, and assuming there isn't all sorts of junk
software running on the XP Home system that makes rsyncd compete for
the already slow disk subsystem, I would take a look at the rsyncd
installation. (I have seen active Antivirus make rsyncd max out a
processor)
The XP Home system should be fairly clean, but the rsyncd installation is probably about 3 years old. Unfortunately, the Linux distro on the server has gone out of date (I think it's Ubuntu 7.04 or something) and lot of tools that I would use to measure performance on the server side (e.g., iostat, etc.) were not and cannot easily be installed at this point. Monitoring Windows performance should be pretty straightforward, though.
I have seen some poor results on some Windows XP systems with
Cygwin myself as well, using the aged 2.6.8 rsyncd package distributed
from the BackupPC sourceforge site.
There are various guides on getting a more recent cygwin/rsyncd
installed on Windows, or for a quick switch-and-test you can install
DeltaCopy on the XP Home system for a quick trial run.
Are you saying that the download available from the sourceforge site is not the best option for giving Windows XP rsync superpowers? I've never looked at DeltaCopy; is there consensus that that's a better option than the sourceforge rsyncd/Cygwin?
On the hardware for the new server, I pretty much agree with Les - use
single disk or RAID1 for an uncomplicated fast setup. Stay away from
RAID5.
Drive spindle speed is the main thing you want to focus on, especially
if the server will be backing up multiple clients simultaneously.
There's an idea! I have a small number of clients; perhaps I should allow BackupPC to back up only one at a time!
