[plug] file transfer performance linux/windows and filezilla

[Denis Brown]

Dear PLUG list members,

Am I expecting too much "performance" from the ssh layer during secure file 
transfers?   To clarify...

Linux (Debian GNU/Linux woody) transferring large files to/from Windows 
machines (NT4WS) over a 100Mb/s utp network with FileZilla as the Windows 
client.   Protocol is ssh(2).   Performance is woeful - like about 50Kb/s 
rising to 100Kb/s occasionally.   If I use ftp rather than ssh as the 
protocol, I get 7+ MBytes/sec so it looks like the network infrastructure 
is happy.

NICs set to force 100Mb/s full duplex.   D-Link non-managed 10/100 switch 
(tried both 16-port and 5-port devices) both connected to the site LAN and 
disconnected from the site LAN.   MTUs set to 1500, sane-looking send/recv 
windows, buffer sizes, etc, etc.   FileZilla set to non- or compressed mode 
makes no difference to transfer performance.

Linux -> linux using scp gives 10MByte/S so I assume there is some overhead 
in the ssh implementation.   Windows -> windows using only tcp/ip protocol 
stack and mapped drives gives probably close to wire speed.   On the 
windows side a netstat -e shows nothing obvious.   On the linux side, 
ifconfig likewise shows nothing apparently amiss.   Also "top" shows the 
linux boxes are not even thinking about raising a sweat.   Process ssh is 
taking maybe 9% cpu but these are fairly grunty machines.

So... what level of performance (or performance hit) should I expect with 
ssh for secure transfers?   And importantly, are there any tuning 
parameters that can allow me to continue to use ssh without having my 
people drink lots of coffee waiting for their files to up/down load?   For 
example the ssh (login) client on Linux will accept a -c parameter to 
define which cypher is being used.   By default this seems to be 
3des.   Blowfish is claimed to be a faster algorithm but I see no way (in 
FileZilla at least, or the associated PuTTY) of forcing a particular 
cypher.  In PuTTY on a session-by-session basis the preferred encryption 
algorithm can be set, but this doesn't seem to carry over to FileZilla.

TIA,
Denis