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

Jens Axboe
2004-01-31T17:42:13Z

On Sat, Jan 31 2004, Philip R. Auld wrote:
> Rumor has it that on Sat, Jan 31, 2004 at 10:30:37AM +0100 Jens Axboe said:
> > On Fri, Jan 30 2004, Joe Thornber wrote:
> > > 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.
> >
> > I suspect the problem really isn't that huge in 2.6, since most
> > performance file systems are using mpage or building their own big
> > bio's. So in a sense, some of the merging already does happen above dm
> > (and the io scheduler).
>
> Out of curiosity, where does raw io fit into that in 2.6?

raw io (or O_DIRECT io, same path) should work even better, always send
out bio's as big as the underlying device can support.

--
Jens Axboe