Perlbal reproxied downloads stalling

[Sam G]

Hi all,

I have perlbal installed on a Centos 4.4 x64 dual Opteron server w/ 4GB  
RAM, and am reproxying from a webserver to read files from a clustered  
storage backend running Apache/DAV. When I do a reproxied download, things  
seem to go well until a few megabytes into the file; then, the download  
seems to slow down sharply then hang. It will happen at different parts of  
the file, but the speed always starts out strong (500kb/s to 2mb/s,  
depending on the connection I'm downloading from) but after 10 seconds or  
so comes to a halt. Sometimes it'll slow way down, speed back up, but then  
slow down again, finally hanging. This happens for virtually any large  
file.

I've tried both 'ioaio' and 'none' for the aio_mode parameter (Linux::IO  
won't pass tests), but same thing happens in both cases. I can pull from  
the storage to the perlbal machine no problem with HTTP wget, at about 30  
MB/s uninterrupted. As the reeproxied download happens, perlbal CPU usage  
never goes above 1%. I have the default buffer settings; have tried  
tweaking a little but to no avail.

Anyone have any ideas why this might be happening?

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