Should using the software update service be faster for the clients then downloading from apple?

Question

I've got about 25 clients, a mixture of Snow Leopard and Lion systems in the office. I've recently turned on the Software update service on my snow leopard server (10.6.8, mac mini) and have a transparent server setup for the software updates service (dns redirects through the mini). All the machines see the mini and I believe they are pulling updates from it when the client runs their software update. I haven't noticed any real speed differnce though from pulling updates from the mini vs pulling from apple (though I have noticed less internet congestion).
Should this be faster because it's a local network transfer or not?
Thanks!

Answer 1

I'm a little concerned by the statement:
dns redirects through the mini
Are you saying you're masking Apple's DNS so that requests for swupdate.apple.com end up on your machine? That's the wrong approach. You should be setting the client's preferences to load from your server instead of Apple's.
In either case, there are three components to running Software Updaate.
1: download the catalog of available updates and compare what's installed to the list to identify which updates are needed
2: download the appropriate updates
3: install the updates.
Of the three steps, downloading the catalog is a lightweight process - the index is only a few hundred KB, so the difference in loading this from your server vs. Apple's is minimal. Additionally, this won't make any difference in the amount of time it takes the client to scan for which updates are needed since that's all work performed locally on the machine.
The only step that will be significantly faster is the actual downloading of available updates. These should happen at LAN speeds, rather than your internet connection speed (which is, presumably, slower), but then again, most updates are fairly small - a few megabytes is typical.
However, if no updates are available, or if they're only small, you won't see much difference in time between local and remote. The main advantage of using a local software update server is that you only need to download the updates from Apple once, rather than once per client.