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

Damien Miller djm at
Sat Mar 22 14:43:21 EST 2003

On Sat, 22 Mar 2003 11:58 am, 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?

What sftp client are you using? I get consistent 2.8Mbps with OpenSSH client & 
server with arcfour cipher.

Also, please retry your tests with a recent version. In a couple of days, you 
have 3.6p1 to try...


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