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
