A fix for Leopard’s messed up “Self-Tuning” Networking
Since switching to Leopard on my server earlier this week, I have noticed that file transfers over the Ethernet LAN at work are insanely slow. I frequently synchronize files (over AFS File Sharing) over an Ethernet LAN between my server and my MacBook Pro. My MacBook Pro has been running Leopard for several months while my server was running MacOS 10.4.11 until this week. Having been happy with Leopard on my MBP, I decided to upgrade my server. Since then, file transfers between the two computers have been a royal disaster. When I initially connected I was getting speeds of up to 1.5 MB/s, but it quickly drops to 30KB/s or less. This was much less than the 10MB/s speeds I was typically seeing before upgrading my server to Leopard. I couldn’t quite figure out the pattern. It did seem the speed uploading files to my server was not as affected as downloading from my server.
Given the fact I didn’t see any file transfer issues between the two computers before upgrading the server to Leopard (MacOS 10.5.2), I suspected the issue was solely with the server (or possibly due to the communication between two computers running Leopard). On a hunch that the “self-tuning” networking heralded (quietly) on Apple’s Leopard Features page might be the problem, I tried to turn it off by tinkering with the “Advanced” settings in the Network Preference Pane. Specifically I changed the settings to look like this:
Notably, I forced the configuration to be manual (instead of “Automatic”), I set the “Speed” to “100BaseT” which is my LAN’s speed (instead of “autoselect”), and I set the “Duplex” to “full-duplex” without “flow control”. I left the “MTU” at “Standard (1500)”.
Making these changes seems to have done the trick. For the last hour my network has maintained speeds of about 10 MB/s on download, something it hasn’t been able to do for the last few days. I suspect Apple has some work to do on their “self-tuning” Network code.
[Followup Post: Yes,this pretty much fixes my network slowdowns. I just did some Bandwidth tests online, I'm back up to my pre-Leopard speeds.]
