16k read 64k write chunk size RAID 5 RAID 6 RAID 5 RAID 6 128k 492 497 268 270 256k 615 530 288 270 512k 625 607 230 174 1024k 650 620 170 75It strikes me that these numbers are meaningless without knowing if that is actual data-to-disk or data-to-memcache-and-some-to-disk-too. Later versions of 'dd' offer 'conv=fdatasync' which is really handy (call fdatasync on the output file, syncing JUST the one file, right before close). Otherwise, oflags=direct will (try) to bypass the page/block cache. I can get really impressive numbers, too (over 200MB/s on a single disk capable of 70MB/s) when I (mis)use dd without fdatasync, et al. The variation in reported performance can be really huge without understanding that you aren't actually testing the DISK I/O but *some* disk I/O and *some* memory caching.
I did these benchmarks with 32GB of data on a machine with 1GB of RAM, therefore the memory cache contribution should be small.
Kind regards, Thiemo - 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
