[lug] Timing Out on large Internet copies

[David Morris]

On Wed, Sep 15, 2004 at 04:42:18PM -0600, Jani Averbach wrote:
> On 2004-09-15 17:34-0400, Gordon Golding wrote:
> > 
> > We have remote servers.  We want to back up some data.  
> > 
> > We are using the SSH window from a PC to copy files off the servers across the Internet.
> > 
> > Our network and the servers remote networks are fast, but the copy
> > always times out - it's some hours worth.
> > 
> > Any thoughts on causes?  Are there settings in Secure Shell?
> > Settings on the Servers?  I'm used to unused connections timing out
> > after an hour, but not active ones.

SCP has VERY low tolerance for packet loss....if the time
till crash is not regular, it might just be busy internet
traffic causing the connection to break (which is almost
guaranteed to come up if you have a several-hours scp
session, even using a fast link).  Also, if you're
saturating the connection on one side or the other (say, T3
to DSL, DSL maxed) keep-alive packets have a hard time
getting through which can cause an SSH connection to
timeout.  Same thing can happen if one side has router
problems....test if a normal SSH shell connection sitting
idle will randomly loose its connection for no apparent
reason before the shell timeout occurs.

I've also found that not all systems see an SCP transfer as
activity worthy of preventing a shell timeout.

You might consider using rsync with ssh for the transport.
That would allow you to auto-retry the transfer and resume
from the place where it lost the connection.

--David