WinSCP mega-slowness

Xn Nooby xnooby at
Mon Feb 20 01:27:23 PST 2006

Well, it's good to know I'm not the only one seing this. Right now both
machines are running FreeBSD, since I gave up on waiting for Windows to copy
the files.  The CPU load on Window when sending  1 meg per second is usually
about 30%, while the Unix box is only at 1-2%.  When I have 2 Unix boxes
sending/receiving, I think the load is like 4-5% on both.  I'm building a
bunch of packages right now, so I can't get the exact number.  I could try
the openssh patch later in the week, that would be great if there was a
unix-side fix for this. Of course as I run FreeBSD more, and Windows less,
the problem will go away, too.


On 2/20/06, Andrew Pantyukhin <infofarmer at> wrote:
> On 2/20/06, Xn Nooby <xnooby at> wrote:
> > For about a year I have noticed that whenever my Windows boxes talk to
> my
> > Unix boxes, they communicate at about 1/10 normal speed. I copy lots
> (300GB)
> > of large files back and forth between machines as I try different OS's,
> and
> > I always see this.
> >
> > Specifically, if I copy from FreeBSD to FreeBSD, files transfer at 11
> megs
> > per second.  Between FreeBSD and Linux, at about 8 megs per
> second.  Between
> > FreeBSD and Windows, about 1 megabyte per second.  This is on identical
> > hardware.  I've told other people about this, and they usually say I
> must be
> > doing something wrong, but recently a friend of mine upgraded a Windows
> box
> > to SP2, and now they are getting this same slowness.  When I copy from
> > Windows to WIndows (XP or W2k), I get 11 megs per second.
> >
> > My machines are two P4's with gigabit NICs, and I'm using WinSCP and
> > (somtimes) pscp.exe on WIndows to talk to sshd on FreeBSD.  It's always
> a
> > shock when I have to copy my data to WIndows, and it takes 30 hours
> instead
> > of 3.
> >
> > Does anyone else ever see this slowness when copying files between
> FreeBSD
> > and Windows?
> >
> > Is Windows maybe capping the transfer speed when it talks to Unix?
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> It is very certainly a known issue. Not that its specifics and
> origins are clearly known, but most of us stumble upon it
> sooner or later. You can usually achieve wire speed only
> between two OSes of a kind. TCP/IP optimizations are
> very important here: if they differ, performance plummets.
> Depends on a multitude of things from quality of NICs to
> weather in your area. I've never been able to get more
> than 70Mbit/s between FreeBSD and Windows XP. I
> always get 90-100Mbit/s between two BSDs or two Win's.
> As for your case, 1MB/s is a serious limit. What can you
> tell us about CPU load? Interrupts? Can you try this:

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