On Wed, 14 Mar 2007, Neil Brown wrote: > On Tuesday March 13, gergely@xxxxxxxx wrote: > > On Tue, 13 Mar 2007, Tomka Gergely wrote: > > > > > On Tue, 13 Mar 2007, Justin Piszcz wrote: > > > > > > > Have you tried increasing your readahead values for the md device? > > > > > > Yes. No real change. According to my humble mental image, readahead not a > > > too useful thing, when we read 1-4 thread with sdd. The io subsystem > > > already reading with the possible maximum speed, so don't have time to > > > read ahead. Correct me, if i wrong. > > > > I was wrong, readahead can speed things up, to 450 MBps. > > Can you tell use what read-ahead size you needed? > > 15 drives and 64K chunks gives 960K per stripe. > The raid0 code should set the read-ahead to twice that: 1920K > which I would have thought would be enough, but apparently not. blockdev --setra 262144 /dev/md0 gives me 650+ MB/s with 4 threads (paralell running sdd). Lower values give lower speeds, greater values not giving higher speeds. -- Tomka Gergely, gergely@xxxxxxxx - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
