[gentoo-user] an efficient network file system on slow connection, which one to choose?

Hello. I am trying to find out what's the best network file system (in
general, like afs, coda, nfs, cifs) fits. We have our two offices
connected to each other through a connection average at 15 to 20 KB/s
with ping-delay  less than 100ms and sharing files on the server in one
of the office.

Currently we use NFS, but it's unacceptably latent ("ls" takes 6
seconds, so does opening and saving a file). It seems to be protocol
overhead because even small directories and small files take 6 seconds
to open. By "latent", I don't know how to describe this better, I mean,
for example, if we do a cp, we are satisfied at how long time it takes
to transfer the file, but not satisfied with the time it awaits before
the transfer starts.

I guess what we need is a network FS that:

   1. cache as much as possible and update cache as less frequently as
      possible. I do think cache greatly helps efficiency because most
      of time we only work in several fixed directories, with several
      fixed files. We re-list them, re-read the, re-write them, so the
      traffic of requesting new data was really low. Mostly everybody
      here work in their own directory, it's very rare someone touches
      files of other people, so one really doesn't mind if "ls" output
      the list of files in the directory 30 minutes ago, as long as his
      own changes are updated (e.g. if he created a file himself it
      should appear in 'ls').
   2. less protocol overhead;
   3. maintain a tcp connection. I guess this is good, because then if I
      do a 'ls' I don't have to wait for a new connection to be
      established. But I am naive here about network knowledge.
   4. It is possible to re-establish connection efficiently. this is
      because our ISP is not good at maintain a tcp connection longer
      than 1 hour, the server/client better has the knowledge how to
      re-connect by themselves without forcing user to wait.


Before I try afs, coda, cifs one by one, I'd like to hear opinions from
you especially if you tried other file systems already, your comment is
very appreciated. Thanks in advance!

By the way we have the current setup because we have a powerful
development server runs the system-in-develop in office A, and people in
office B wish to save the trouble and human hour cost of also
maintaining their own development server, by using network file system
to directly work on the other office's development server. We develop
using svn. Any alternative idea other than a network file system is also
very welcome here. Other idea I haven't tried is ftpfs and sshfs, but
don't know if they perform better.