[clug] SCP from Windows to Linux incredibly slow
Paul Wayper
paulway at mabula.net
Tue Aug 10 01:53:48 GMT 2004
At 08:36 PM 8/08/2004 +1000, Tony and Robyn Lewis wrote:
>On Sun, 2004-08-08 at 19:21, Peter Lavender wrote:
> > I have read the other replies, and most are looking at the network layer
> > as a possible problem, which is a fair thing to do, however I suspect
> > that you will find it isn't the problem here. (Of course I could be
> wrong).
>
>Perhaps the following might be worth a try (though it's guesswork from
>me)
>
>1. does anything noticable happen to CPU usage on your win32 box when
>you use pscp?
No, the pscp or WinSCP process are using negligible amounts of CPU time on
both machines.
>2. if you sniff packets between them, you might be able to see a pattern
>of who is being tardy with their responses
Good idea. Let's see...
Well, interestingly, I got one transfer to go at 2MB/sec - all the rest
seem to be sending one packet every five seconds or so. I have no idea
what the difference was, I'm just tracing through the packets in ethereal now.
>3. is there any unanswered DNS going on that it's timing out on?
Don't think so. What's really odd is that it seems to start out going at a
reasonable clip and then after two to three seconds slows down. My best
guess is that it's an emergent problem to do with Nagle's algorithm, which
makes sense for character-by-character typing but somehow gets into a
feedback loop when sending lots of data.
I read of an interesting attack on TCP where, by sending choke notices at
exactly the right interval (around one packet per second) you could
effectively DOS any port on a router by convincing it that the other end
was saturated. It's made me wonder if this sort of timing problem is involved.
>4. is putty's ssh similarly slow (you might test it by doing something
>like ls -laR / and seeing how fast it scrolls)?
Not at all. Seems to be full speed.
>5. if you boot from knoppix, does the scp work better?
No idea - haven't download Knoppix to try it.
I'm getting Samba working between the two boxes, and that certainly moves
data around like greased bowling balls on ice - i.e. much faster. But it'd
still be nice to know what the problem is - it should work...
Thanks all,
Paul
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