file transfer size limit

I've been moving large files (several gb) via scp, and would like some
advices.

1. I'm transferring files via dd on ssh : 

/usr/local/bin/tar cvfz - mydirectory | /usr/local/bin/ssh
user@remote_host dd of=/backup/backup.tgz

This used to work but when about 30 gb worth of files were added, the
transfer stopped after finishing about 8 gb.

I haven't logged what's happening, but could there be a timeout issue? 
(The network is 100mbps but I get at best 2 mb when there's no office
traffic.) For example, would the above transfer stop after 2 hours (grace
time)?

2. Cygwin's tar cannot read tar files sftp'd from a unix server through
ssh.com's sftp client, while the same tar file on the unix server reads it
OK. I suspect the sftp'd copy got corrupted by ssh.com's sftp client.

There are other unexpected irregularities like some large tar files
hanging near the end of transmission and aborting, while moving these
large file between windows and unix machines.



Is there a documentation for known problems with different sftp/scp
implementations?



Regards,

Ben Kim
Developer
http://benix.tamu.edu