[OpenAFS] Read-Write Disconnected Mode - How does it work?
Sat, 31 Jan 2009 23:55:37 +0000
On 31 Jan 2009, at 23:34, William McCabe wrote:
> The latest version of openafs 1.5.57 can use volumes in a
> disconnected read-write mode.
Indeed it can. The work was done by Dragos Tatulea as part of last
year's Google Summer of Code.
> Where can I find some documentation for how to use this feature? Is
> the feature stable? What are the bugs?
There's not much user documentation available. Disconnected
operations is still under active development - whilst I'd love to get
feedback from power users who are testing it, it probably isn't
entirely ready for production use. The major showstopper here is that
we don't have a mechanism for preserving the state of the cache
across machine reboots. This means that if you reboot your machine
for any reason whilst disconnected, you lose all of the changes made
whilst in the disconnected state. Obviously, this is a significant
data loss issue and one that needs to be resolved before its ready
for widespread use.
That said, of the currently known bugs in disconnected, which are
tracked in RT at http://rt.central.org/rt/Ticket/
Display.htmlid=124148&user=guest&pass=guest there don't appear to be
any other significant data loss issues, and I'd be very grateful to
hardy souls who wish to try it out and provide additional bug reports.
The user interface is currently pretty primitive (the other major
issue that we need to resolve before it's 'done').
Before disconnecting, you must first prime your cache with all of the
files you wish to use whilst disconnected. Eventually, we will have a
pinning mechanism which will allow the cache manager to do this for
you. I typically prime my cache by doing something along the lines of
find . | xargs cat > /dev/null
Then, you can take the cache manager disconnected by running (as root)
fs discon offline
You may then read and write files in the primed set as you see fit.
When you are back on a decent network connection, you can go back
online by running, as root, and
with appropriate tokens:
fs discon online
This may fail either due to conflicts on the server, or due to
transient errors such as connection timeouts. If it does so, you can
retry simply by running the command again. Server conflicts currently
have to be repaired by hand. If you're in a situation where you just
can't fix the problem, and you're happy to discard the data, 'fs
discon online -force' will reconnect you, throwing away any stored
I've so far run a number of file system test utilities against
disconnected mode, as well as using it for some day to day work, and
a large number of package builds. I'm not currently aware of any way
to break the current code. There are some additional fixes in CVS,
over the 1.5.57 release, so if you are interested in testing, using
the tip of the 1.5 branch is a good place to start.
If you do try it out, please do let me know how you get on!