[OpenAFS] vos release fails -- bandwidth too low?

Chaz Chandler clc31@inbox.com
Sun, 31 Aug 2008 16:12:12 -0800

Hi all,
We have a multi-site setup with OpenVPN and are evaluating technologies =
for serving files to local users and across the vpn.  From what I've read, =
OpenAFS is a good match for our low-bandwidth vpn links, but in the actual =
implementation it isn't working out.

We've implemented a bridged OpenVPN multi-site network via UDP.  The vpn =
has not been specifically optimized for bandwidth, but that is probably a =
discussion for another forum.  We are currently seeing about 26KBps =
sustained across the links.
Our OpenAFS trial setup has two file servers, one with an RW volume and =
both with RO volumes of the RW one.

The Problem:
In our simple tests, we made a change to the RW volume and attempted a =
release.  In the case where both servers are at the same site (and =
therefore have the full lan bandwidth), a vos release works perfectly.  In =
the case where the two servers are at different sites, the vos release =
fails for all practical purposes: that is, it never finishes and there =
doesn't seem to be any serious amount of communication across the vpn =
between the two servers.  There are no relevant error messages in the afs =
logs, except for the every 30-second info/warning messages about the vos =
release continuing.  There are obviously firewalls involved when operating =
across the vpn, but it is a fully-bridged network and an analysis of =
dropped packets at the firewalls and the file server machines does not =
show anything related to AFS.

Our questions:
Where should we go from here?  Is our vpn bandwidth too low to support =
openafs?  Is there some additional analysis to perform?  Is there a better =
afs setup to use?  Any hints on vpn tweaks to resolve the issue?

Thanks in advance,
-Chaz Chandler