On Sun November 1 2009, Andrew Dunn wrote: > Are we to expect some resolution in newer kernels? I assume all of the new per-bdi-writeback work going on in .33+ will have a large impact. At least I'm hoping. > I am going to rebuild my array (backup data and re-create) to modify the > chunk size this week. I hope to get a much higher performance when > increasing from 64k chunk size to 1024k. > > Is there a way to modify chunk size in place or does the array need to > be re-created? This I'm not sure about. I'd like to be able to reshape to a new chunk size for testing. > Thomas Fjellstrom wrote: > > On Sat October 31 2009, Jon Nelson wrote: > >> I have a 4 disk raid6. The disks are individually capable of (at > >> least) 75MB/s on average. > >> The raid6 looks like this: > >> > >> md0 : active raid6 sda4[0] sdc4[5] sdd4[4] sdb4[6] > >> 613409536 blocks super 1.1 level 6, 64k chunk, algorithm 2 [4/4] > >> [UUUU] > >> > >> The raid serves basically as an lvm physical volume. > >> > >> While rsyncing a file from an ext3 filesystem to a jfs filesystem, I > >> am observing speeds in the 10-15MB/s range. > >> That seems really really slow. > >> > >> Using vmstat, I see similar numbers (I'm averaging a bit, I'll see > >> lows of 6MB/s and highs of 18-20MB/s, but these are infrequent.) > >> The system is, for the most part, otherwise unloaded. > >> > >> I looked at stripe_cache_size and increased it to 384 - no difference. > >> blockdev --getra reports 256 for all involved raid components. > >> I'm using the deadline I/O scheduler. > >> > >> Am I crazy? Is 12.5MB/s (average) what I should expect, here? What > >> might I look at here? > > > > I can't say I see numbers that bad.. But I do get 1/3 or less of the > > performance with .29, .30, .31, and .32 than I get with .26. I haven't > > tried any other kernels as these are the only ones I've been able to > > grab from apt ;) > > > > I get something on the order of 100MB/s write and read with newer > > kernels, with really bursty behaviour, and with .26, its not as fast as > > it COULD be, but at least I get 200-300MB/s, which is reasonable. > > > > Now if your two file systems are on the same LVM VG, that could have an > > impact on performance. > -- Thomas Fjellstrom tfjellstrom@xxxxxxx -- 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
