showdown transfering files with scp

Alex Zbyslaw xfb52 at
Thu Feb 9 04:01:24 PST 2006

mark.jacobs at wrote:

>I was using scp to copy several large (300-800mb) each files between two
>Freebsd machines. Both are on the same hub, 100MB Ethernet connection.
>The source box is FreeBSD 5.4 stable at a late October build date. The
>target is running 6.0 stable at a current build date.
>The first three files showed a transfer rate of about 3mb/sec and
>transfer took about a 5-7 minutes for each file. After the third one
>however the transfer rate dropped to 100-200 KB/sec. There was nothing
>else going on in the internal network at the time.
scp can be surprisingly crap and slow.  If the machines are both 
internal try using ftp and see how that does.  If that's slow too then 
you have a problem :-)  If it isn't slow, then try the ssh-hpn port 
which, among other things, supports a -z flag to scp which turns off all 
the encryption after the initial authentication.

It's also possible that one of the machines got loaded with something 
else around the time of your slowdown and it couldn't keep up the the 

Other things to try:
    1) repeat what you did and see if it happens again.  If it doesn't, 
then there was something going on the first time.
    2) If it does happen again, try transferring the files individually, 
inside a for loop perhaps, and see if the problem persists.  If it does, 
try ssh-hpn and see if that works better.



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