How do remote filesystems (nfs ssfhs) handle remote-to-remote copies?

Question

After working with a few large files over sshfs, one question started dwelling in my mind.

Suppose I have a sshfs (or NFS for that matter) mount on ~/remodetir and I want to do something like

cp ~/remotedir/foo ~/remotedir/some/weird/path/bar

Does sshfs (or NFS) handle it in a smart way or do they transfer the file back-and-forth just because the cp command is running in my local CPU?

@JimB, like with SMB where the client can ask the server to perform a local copy using RPC. — Zoredache, Jun 04 '12 at 23:28
I am almost 95% certain that SSHFS is pretty dumb, but I don't know much about the NFS internals. — Zoredache, Jun 04 '12 at 23:29
@JimB yes, a good definition of "smart way" would be the one given Zoredache, above. — Elton Carvalho, Jun 05 '12 at 00:00
There was a discussion on whether it is possible to [copy remote files on nfs without round-trip](http://superuser.com/q/337778/128116) on superuser.com. The conclusion was that it is not possible in general, but tools exists to support this. — Dima Chubarov, Jun 05 '12 at 06:59
Thanks, @DmitriChubarov I guess that the same would be valid for `sshfs` for similar reasons. — Elton Carvalho, Jun 05 '12 at 14:56

84104 · Accepted Answer · 2012-06-05T16:01:33.847

4

sshfs makes local mv calls for mv.

I assume this is similar for cp.

Not sure if this is the case if the remote sshd restricted to internal-sftp.

edit:

File flows through local machine for cp as well (confirmed with network traffic).

$ sshfs -V
SSHFS version 2.4
FUSE library version: 2.8.6
fusermount version: 2.8.6
using FUSE kernel interface version 7.12

edited Jun 05 '12 at 16:01

answered Jun 04 '12 at 23:45

84104

So the local call for `mv` really means data transferred from the server to the client and back? Because, AFAIK, `mv` only messes with file handlers, or hardlinks, if you prefer, so the size of the file moved by `mv` doesn't matter so much, as long as filesystem borders are not crossed. – Elton Carvalho Jun 05 '12 at 00:02

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