Transfer rate issues with OpenSSH SFTP Server - Verified on Mac OS X 10.2.X and FreeBSD 5.0

Scott Burch scott.burch at
Tue Mar 25 05:49:29 EST 2003


I have dealt with this issue and discovered that it has a lot to do with
the compiler used to build openssh (or possibly the compiler flags).
Below is some discussion I had with people inside my company regarding
this issue and how I resolved the problem on Solaris: (If you want more
details let me know.)

(Internal discussion of this issue below)

I had a discussion with [name removed] regarding performance issues of
my openssh package; I confirmed there was indeed a problem. I have
discovered that compiling the components with Sun's compiler is the
source of the problem. The version I compiled with gcc 3.2 works great.
This morning I did a test from my Windows 2000 PC with Secure FX 2.1
transferring the same 137 MB file throughput was over 430
KB/s; obviously Solaris w/openssh client is much faster than Secure FX
on our 2000 builds, but the throughput I got was almost 2x faster than
[name removed] transfer (using Secure FX on his laptop) to [server name
removed] (running's 2.2.0).


> -----Original Message-----
> From: Burch, Scott 
> Subject: You can't beat this openssh performance
> sftp from a machine (Sun servers running Solaris 8) on one subnet to
> Transferred 137 Megabytes in 60 seconds which translates to:
> 2338.133333 kilobytes/second
> I'll test with securefx in the morning. The client and server 
> in this test are running openssh 3.4p1 components built with 
> gcc 3.2. [name removed] demonstrated that the same software compiled 
> with Sun Developer 7 performed miserably. I will test with 
> securefx in the morning, to ensure that it is not an issue 
> with securefx. [name removed] and I saw miserable performance between 
> securefx and openssh 3.4p1 compiled with Sun Developer 7.

(End Discussion)

On Mon, 2003-03-24 at 11:45, James Puckett wrote:
> I have been dealing with they same problem for at least a year now, and 
> probably should have brought it up sooner. I use OpenSSH at work and at 
> home on Apple, x86 and Sun systems ranging from from a K6-III/400 to 
> uber-v880s, and no matter what system I use or which user is tranferring 
> files, the throughput I get from the sftp server is pathetic. I work 
> around this problem by just using scp wherever possible, because scp 
> does *not* suffer a noticeable performance hit.
> If this is just a simple cipher selection option, it needs to be 
> documented somewhere obvious, because users and sysadmins just are not 
> aware of it.
> -james
> John Stockdale wrote:
> > First, I have what I consider to be decent experience with SSH, and have
> > been running VanDyke's VShell SSH server for considerable time under
> > Windows 2000/XP. Recently, I have been working with Mac OS X and FreeBSD
> > and have been using OpenSSH 3.4p1 The sftp server seems to have major
> > issues when serving files, specifically, if one data stream is used the
> > transfer rates fluxuate between 80 and 200 KB/s. Keep in mind that this
> > is over a 100Mbit switched link. If multiple transfers are performed at
> > once over one login session, the transfer rates of both files increases
> > to 800-1000KB/s still below what it should be but substantially better.
> > 
> > Performing similar transfers in the other direction, using the VShell
> > sftp server and sftp clients on the other boxes, the transfer rate is in
> > the order of 3000-4000KB/s. These are all modern boxes that should
> > beable to do AES-256/Twofish at more than adequate rates to sustain the
> > transfer, so the only thing I can think of that would be causing the
> > problem would be some bug in the OpenSSH sftp server.
> > 
> > Any thoughts?
> > 
> > Thanks
> > 
> > -John
> > 
> > _______________________________________________
> > openssh-unix-dev mailing list
> > openssh-unix-dev at
> >
> > 
Scott Burch <scott.burch at>

More information about the openssh-unix-dev mailing list