AFP Performance Spike and Drop on Leopard

[jmah]

Hi,

Since going to Leopard, I’ve had strange AFP behavior. When copying files, the transfer will start at normal speed (~10MB/s), but after it’s copied somewhere between 20MB and 50MB it suddenly drops off to a trickle (less than 100KB/s). It will stay that way for the rest of the file. Copying with SCP is fine, maintaining the peak speed throughout. I’ve taken a [url=http://screencast.com/t/GtMIxgK3C97]screencast that shows the issue[/url].

I’m connected over Ethernet; both server and the client are running 10.5.2. I just checked, and I [i]don’t[/i] get this with a Tiger client (10.4.11), but I do with Leopard clients. I don’t see any relevant entries in the AFP or system logs on the server.

Does anyone have any ideas? Thanks!

[khiltd]

10.5.2 is known to do this on Intel machines. Running: [code]sysctl -w net.inet.tcp.delayed_ack=0[/code] on the client fixes it for some people, but not others. If it [i]does[/i] work for you, I’ve created a LaunchDaemon installer which will run the command for you on every login so you don’t have to continually reset it:

[url]http://www.khiltd.com/Downloads/DelayedAckHack.zip[/url]

Just remember to pull it out once Apple fixes their autotuning TCP/IP silliness in a hopefully forthcoming update.

[jmah]

Setting delayed_ack to 0 cut transfer speed by quite a bit (30-40%), but it maintains that speed for the entire transfer, so it’s far better than the status quo. If there is no other answer, that will have to do for now. Thanks khiltd.

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