On Mon, Jul 26, 2010 at 09:37:20AM +0000, Marco wrote: > > > >> doing a simple performance tests i obtained some very unexpected results: if > >> i issue hdparm -t /dev/md2 i obtain 61 - 65 MB/s while issuing the same test > >> directly on the partitions which compose md2 (/dev/sda3 and /dev/sdb3) i > >> obtain 84 - 87 MB/s. I didn't expect a so big difference between md2 and one > >> of its member. What can cause this difference ? > > > >Maybe their read-ahead settings are different? > >Check out "blockdev --getra /dev/md2", and compare that with the same > >setting of the member disks. You can experiment with changing it by using > >"--setra" as well. > > Hi Roman, > thank you for your hint, I verified the read-ahead settings and they are the > same for all the block devices involved in the test: the value is 256 for all > /dev/sd?? and for all /dev/md? > there should be something else which is influencing raid 1 performance. > Have someone of you ever had a similar issue ? Did you try: # Set read-ahead. echo "Setting read-ahead to 64 MiB for /dev/md3" blockdev --setra 65536 /dev/md3 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
