Rumor has it that on Sat, Jan 31, 2004 at 06:42:01PM +0100 Jens Axboe said: > 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. > That size is based on the blocksize? Is there a way to set the block size higher than 512 w/o mounting it? I've gotten really bad rawio performance on 2.4. since I have a limit of 32 sg entries. When Rawio uses a 512 byte blocksize IOs are limited to 16K. Will this still be a problem in 2.6? Thanks again, Phil > -- > Jens Axboe > > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Philip R. Auld, Ph.D. Egenera, Inc. Principal Software Engineer 165 Forest St. (508) 858-2628 Marlboro, MA 01752