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. I would appreciate any coments in this matter. thank you Raz Ben Yehuda - : 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
