Date: Tue, 29 Jun 2004 23:08:17 -0400 From: Bill Moran <wmoran@potentialtech.com> To: Charles Swiger <cswiger@mac.com> Cc: questions@freebsd.org Subject: Re: REPOST: Performance problems with FTP Message-ID: <20040629230817.0f6d230e.wmoran@potentialtech.com> In-Reply-To: <1133CD52-CA07-11D8-99F8-003065ABFD92@mac.com> References: <20040629140231.7b57dedf.wmoran@potentialtech.com> <1187B403-C9FC-11D8-99F8-003065ABFD92@mac.com> <20040629153855.300b3888.wmoran@potentialtech.com> <1133CD52-CA07-11D8-99F8-003065ABFD92@mac.com>
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Charles Swiger <cswiger@mac.com> wrote: <snip> > >> Can you reproduce by moving ftp to a different port #? (Perhaps some > >> quality-of-service thingy is providing different bandwidth by port...) > > > > I haven't tried that, but I forgot to mention that a Debian box located > > right next to the problem box (on the same network) gets speeds equal > > to what would be expected. To me, that ruled out QOS, routing and > > other > > beyond-my-control Internet problems. Again, I'm happy to be corrected > > if there's something here I'm not aware of. > > Well, that does tend to rule out a bunch of issues. Have you tried > changing the MTU of the FreeBSD box down to 1400 or so (or even 512), > just to see whether that does anything? OK. I've had a bit of success here ... By setting the MTU down to ~650, I get the best performance I've seen with this setup (about 27k/sec ... which isn't too bad) I set "SocketOptions maxseg 650" in the proftpd.conf file for now, which seems to help a good bit. But I'm really confused. Why does reducing the MTU improve performance? I would have thought it would hurt performance by increasing the # of packets, thus increasing overhead. I did some captures using Ethereal, and I'm seeing a weird pause (with the MTU at the default) where the client will send three packets, there'll be a pause, then the ack comes back, then three packets, pause, ack ... You'd think that reducing the MTU would make this worse because there's less data in the three packets, thus more pauses, but when I drop the MTU, the pause reduces significantly. There's something with TCP going on here that I don't understand. (Thanks a LOT for your assistance so far!) -- Bill Moran Potential Technologies http://www.potentialtech.com
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