Re: [dm-devel] Re: Is there a grand plan for FC failover?

[Joe Thornber <thornber redhat com>]

On Wed, Jan 28, 2004 at 04:55:34PM -0800, Patrick Mansfield wrote:
> > We had the "where does the elevator go" discussion at the OLS bof.  I
> > think I heard agreement that the current situation of between dm and
> > block is suboptimal and that we'd like a true coalescing elevator above
> > dm with a vestigial one for the mid-layer to use for queueing below.  I
> > think this is a requirement for dm multipath to work well, but it's not
> > a requirement for it actually to work.
> 
> If the performance is bad enough, it doesn't matter if it works.

It would be great to get some benchmarks to back up these arguments.
eg, performance of dm mpath with a simple round robin selector,
compared to a scsi layer implementation.  Lifting the elevator (or
lowering dm) is a big piece of work that I wont even consider unless
there is very good reason; the reason probably needs to be broader
than just multipath too.  Even if we did decide to do this, it won't
happen in 2.6.

- Joe