Parallel transfers with sftp (call for testing / advice)

Peter Stuge peter at
Tue May 5 18:26:48 AEST 2020

Matthieu Hautreux wrote:
> The change proposed by Cyril in sftp is a very pragmatic approach to 
> deal with parallelism at the file transfer level. It leverages the 
> already existing sftp protocol and its capability to write/read file 
> content at specified offsets. This enables to speed up sftp transfers 
> significantly by parallelizing the SSH channels used for large 
> transfers. This improvement is performed only by modifying the sftp 
> client, which is a very small modification compared to the openssh 
> codebase. The modification is not too complicated to review and validate 
> (I did it) and does not change the default behavior of the cli.

I think you make a compelling argument. I admit that I haven't
reviewed the patch, even though that is what matters the most.

I guess that noone really minds ways to make SFTP scale, but ever since
the patch was proposed I have been thinking that the paralell channel
approach is likely to introduce a whole load of not very clean error
conditions regarding reassembly, which need to be handled sensibly both
within the sftp client and on the interface to outside/calling processes.
Can you or Cyril say something about this?

And another thought - if the proposed patch and/or method indeed will not
go anywhere, would it still be helpful for you if the sftp client would
only expose the file offset functionality? That way, the complexity of
reassembly and the associated error handling doesn't enter into OpenSSH.

Kind regards


More information about the openssh-unix-dev mailing list