WinSCP mega-slowness

Andrew Pantyukhin infofarmer at
Mon Feb 20 00:00:26 PST 2006

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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