[OpenAFS] Re: Disconnected OpenAFS

Jeffrey Altman jaltman@secure-endpoints.com
Tue, 25 Sep 2007 10:37:52 -0400


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John Tang Boyland wrote:
> I would expect that the simplest model for disconnected AFS
> is to simply serve what's in the cache readonly.  That would already
> be a huge step up from what we have now and while it would serve
> old files that have since been changed, by preventing writes, it
> avoids most of the inconsistency problems.  If there's additionally
> a reminder that AFS is "disconnected" then I don't see why the
> remaining consistency issues would be problematic.  In particular,
> readonly means you can't lock the file.
> 
> John

This is not sufficient because the cache manager does not cache files
and directories but chunks of files and directories.  You can't be sure
that you will have all of the chunks that the application might require.
If you don't, then the app crashes.

For Windows, locks are non-optional.  The locks must be issued even when
reading read-only data.  The question isn't can locks be issued but what
is issuing them.  For .readonly volumes, all locks are issued by the
cache manager.  For disconnected files one could make the case that
locks should also be issued by the cache manager.  We have to handle the
transition cases when a file is open in an application when the file
switches from connected to disconnected and back.

If you want the just read what's in the cache functionality, the work
that Simon has already done on the HEAD will give it to you on UNIX-like
operating systems.

Jeffrey Altman

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