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

John Stockdale jstockdale at
Sat Mar 22 11:58:51 EST 2003

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?



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