[OpenAFS] Re: Afs User volume servers in VM's

Jason Edgecombe jason@rampaginggeek.com
Wed, 26 Oct 2011 14:48:32 -0400

On 10/26/2011 11:57 AM, Andrew Deason wrote:
> On Wed, 26 Oct 2011 17:26:55 +0200
> Stephan Wiesand<stephan.wiesand@desy.de>  wrote:
>> Running multiple fileservers on different ports on the same system
>> would be even more efficient. Is this possible or could be implemented
>> (in theory)?
> In theory, of course. You just need a way in the fileserver to specify a
> port, vldb modifications to store a port for the fileserver, and the
> protocol modifications to communicate a port to the vldb and to clients.
> You know, "just" all that :) The prerequisites for the vldb
> modifications have already been discussed a bit on the standardization
> list.
> That would of course limit the amount of clients that can actually
> access that fileserver, since no clients today can do any of that.
>> What would be a great feature to have is a way to keep the server from
>> using more than, say, half of the available threads for a single
>> volume. Would this be feasible to implement at all?
> Sure. Well, sort of. The server can obviously keep track of which calls
> are associated with what volume (and already do post-1.6, for
> -offline-timeout functionality), so if the number of calls is greater
> than "X", we can just not service the request.
> However, the way to do that is to return a VBUSY error to the client
> ("busy; try again later"), which cause the clients to sleep and retry
> after some number of seconds (and make them log those "busy waiting for
> volume" messages). And we only do that after we've obtained some kind of
> reference to the relevant volume, which is after a considerable amount
> of processing has been done. Maybe we could check that a bit earlier,
> but the point is we'd have to receive the call and return an error if
> we're over quota for the volume, which takes some extra processing; we
> can't, like, direct calls dealing with volumes to a certain subset of
> threads or something. But I guess that's probably not a problem; it
> could make things worse in some situations but better in others.
I vaguely recall a hard limit to the number of file servers in a cell. 
That number is 127 if I'm correct.

Is that the case?