Hi Richard: Thanks for sharing your results. So, 565MB/s with 16 disks in an array. It would be nice to see how it scales as we add more disks. What kernel version did you use for this test? Thanks! On Fri, Apr 2, 2010 at 6:14 PM, Richard Scobie <richard@xxxxxxxxxxx> wrote: > Mark Knecht wrote: > >> Once all of that is in place then possibly more cores will help, but I >> suspect even then it probably hard to use 4 billion CPU cycles/second >> doing nothing but disk I/O. SATA controllers are all doing DMA so CPU >> overhead is relatively *very* low. > > There is the RAID5/6 parity calculations to be considered on writes and this > appears to be single threaded. There is an experimental multicore kernel > option I believe, but recent discussion indicates there may be some problems > with it. > > A very quick test on a box here on a Xeon E5440 (4 x 2.8GHz) and a SAS > attached 16 x 750GB SATA md RAID6. The array is 72% full and probably quite > fragmented and currently the system is idle. > > dd if=/dev/zero of=/mnt/storage/dump bs=1M count=20000 > 20000+0 records in > 20000+0 records out > 20971520000 bytes (21 GB) copied, 87.2374 s, 240 MB/s > > Looking at the outputs of vmstat 5 and mpstat -P ALL 5 during this, one core > (probably doing parity generation) was around 7.56% idle and the other 3 > were around 88.5, 67.5 and 51.8% idle. > > The same test run when the system was commissioned and the array was empty, > acheived 565MB/s writes. > > Regards, > > Richard > > -- 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
