i think that a good add to today read balance could be add disk acess_time (1/rpm, 0 for 'non rotational', 1 for unknow) head_distance * acess_time, could allow a better select of disks or mix of 7200/10000/15000 rpm disks maybe it can be read from disk information at assemble time, i don't know if disk speed (rpm) can be read from device block (some disks display information with hdparm and smartctl) it's not a 1000% improvement, it's 1% at high read/write load 2011/5/4 Keld Jørn Simonsen <keld@xxxxxxxxxx>: > On Wed, May 04, 2011 at 09:42:40AM +0200, David Brown wrote: >> raid10,far is better for sequential reads - it gives better-than-raid0 >> performance on average since it will do striped reads from the faster >> outer tracks. And for multi-threaded reads, it should also be a little >> faster than other raid10 layouts (and raid1, which is much the same as >> raid10,near). Since it prefers to get the data from the outer half, you >> get the benefits of short-stroking your disks - faster transfer speeds >> and less head movement. >> >> The cost of raid10,far is greater head movement for writes - but that is >> not the OP's main concern. > > yes, in theory this is so. But two reasons almost eliminates this in > practice. First, the processes do not wait for completion of the IO of > writes, the processes only deliver the data to the file buffer cache of > the kernel, which then periodically flushes the data to the disk drives. > Second, the flushing of the data is ordered so that the collected data > buffers are written as much sequentially as possible to the drives. > This goes for all Linux MD RAID1/RAID10 layouts. Given that random > writes are random over the whole set of drives, for any mirrored > raid1/raid10 layout, the flushing of the data is about the same. > > best regards > keld > -- > 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 > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- 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
