[Linux-cluster] Interfacing csnap to cluster stack

[Daniel Phillips]

On Friday 08 October 2004 15:45, Daniel Phillips wrote:
> On Friday 08 October 2004 15:13, Lon Hohberger wrote:
> > If operating within the context of rgmanager (or another RM), it's
> > probably a good idea to never have the csnap agent directly
> > instantiate a master server as a result of a csnap client request
>
> That's the plan: when an agent receives a request for a server from a
> device mapper target, it just passes it on up the chain, and stands
> by to instantiate a server if requested.

Oh, and if we (temporarily) adopt the dlm EX lock method of choosing a 
server node, then "passing it up the chain" consists of acquiring the 
EX lock.

> > > >     - If a server fails over, the new incarnation needs to know 
> > >       that all snapshot clients of the former incarnation have
> > >       either reconnected or left the cluster.
> >
> > If the clients are part of the csnap master server's state, perhaps
> > that list of clients ought to be moved with the rest of the csnap
> > data.
>
> The rest of the csnap data is persistently recorded on disk.  That's
> one way to go about it all right, let me have a ponder.

OK, ponder done.  Writing the client list into the csnap data vs 
downloading it to all the agents are roughly in the same ballpark of 
efficiency and they both do the job.  They're about the same amount of 
work to implement.  One of them crufts up the metadata and eats a 
little disk bandwidth, particularly at cluster bring-up.  So...

Regards,

Daniel