On 02/12/13 07:22, NeilBrown wrote: > On Tue, 26 Nov 2013 10:58:59 +0000 Pedro Teixeira <finas@xxxxxxxx> wrote: > >> I created a Raid10 array with 16 sata 1TB disks and the array >> performance >> seems to be limited by the md0_raid10 taking 99% of one core and not >> scalling to other cores. I tried overclocing the cpu cores and this lead to >> a small increase in performance ( but md0_raid10 keeps eating 99% of one >> core ). > > Are you really talking about general array performance, or just resync > performance? > > Because md0_raid10 doesn't do much work for normal IO so that should scale to > multiple processors. > I'm not sure that optimising resync to use more than one processor is really > much of a priority - is it? > > NeilBrown I think that depends a bit on whether we are talking about md raid10, or raid1+0. For md raid10, resyncs and rebuilds are always going to take a bit of time - data has to be copied back and forth across the same disks, with a lot of head movement (especially for "far" layout). I don't see that it would take much cpu time, however. And this sort of layout is mostly for small arrays - it gives great performance when you have two drives, and perhaps up to about 4 drives. But after that, people probably want raid1+0 layouts (i.e., raid0 stripes of raid1 pairs). For raid1 + 0, resync time /is/ important - it is one of the reasons people pick it, especially the time to resync a single replaced drive. But again, I can't see how that would take cpu time. I suppose that when doing the initial sync of this 16 disk array, you have to read in all data from 8 disks and write it out to the other 8 disks. That's a lot of IO passing through the cpus, even if there is no calculations going on. But I thought each raid1 pair already had its own thread, so this would be scaled across 8 cores? Is md raid10 limited to just one thread? mvh., David > > >> >> I'm using: >> - a phenom X6 at 3600mhz >> - 16 seagate SSHDs ( sata3 7200RPM with 8GB ssd cache ) >> - 4x marvell 9230 sata3 controllers ( 4 ports each ) pcie 2.0 2x >> lanes. >> - 8GB ram >> - custom 3.12 kernel and mdadm compiled from latest source >> >> what I did to test performance was to force a check on the array, and >> this >> leads to mdadm reporting a speed of about 990000K/sec. The hard disks >> report a 54% utilization. ( Overclocking the cpu by 200mhz increases the >> resync speed a bit and the hdd's utilizartion to about 58% ) >> >> If I do the same with a raid5 array instead of raid10, them resync >> speed >> will be almost double of raid10, the harddisk utilization reported will be >> 98-100% and I can see at least two cores being used. >> >> ________________________________________________________________________________ >> Mensagem enviada através do email grátis AEIOU >> http://www.aeiou.pt >> -- >> 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 > -- 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
