On Sun, Mar 26 2006, Raz Ben-Jehuda(caro) wrote: > It is my belief that the linux elevators are not optimized for > raid throughout. > > Basically when IO initiator generates IO over a single disk he can control > the amount of IOs and this way control IOs latencies. > > This is not the case in raided volumes. > > Example: > > An IO initiator intiates bulks of asynchronous IOs over a raided > volume. since the user does not know the target destination of each IO > he > might cause imbalance over the disks. one disk may become overflooded > with IOs while the other is may starve. So eventually we are ending with > a non balaned raided volume in terms of bad latencies. > > I am trying to deal with this problem by fixing the deadline elevator code > to batch IOs , meaning , when n IOs are reaching the disk, each m deadlined > IOs are sorted and then dispatced. You do realize that the io scheduler resides _below_ the raid personality? So if you want to balance what goes to what io scheduler (and thus, disk), you'd want to mess with the raid personality. -- Jens Axboe - : send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
