Hello, I have created a partitioned raid6 array over 6x1TB SATA disks using the command (from memory): mdadm --create --auto=mdp --level=6 --raid-devices /dev/md_d1 /dev/sd[b-g]. When I run a sequential read test using dd if=/dev/md_d1p1 of=/dev/null bs=1M I get low read speeds of around 80MB/s but only when the partition is mounted. If I unmount, the speed is around 350MB/s. The filesystems I tried are ext3 and xfs. The partitions have been created with gparted, the partition table being of type GPT. If I create normal /dev/sdx1 partitions on each disk and then make a /dev/md1 raid6 array over them, the read speed is ok. I played with different read ahead settings and while they changed the read speed, it's only marginally around the values reported above. Can somebody explain what is the difference when accessing a raw disk when it is mounted or not? Also when playing with those read ahead settings it was not clear how/if the read ahead of the individual disks are taken into account. When setting big values of read ahead, I could see with iostat that tps for the individual disks is double when accessing the mounted disk as opposed to when accessing it unmounted (despite the speed being three times lower). It's like when accessing the mounted partition, it reads some other parts of the disks. I could not find a way to print the blocks read from the individual disks. The sysctl vm.block_dump=1 makes the kernel print the block numbers on the md array but not on the components of the array. The system is debian 5 with kernel 2.6.26-2-686. Thanks for any hint on how to further debug the problem. nicolae -- 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
