On 2011-07-25 19:10, Les Mikesell wrote:
My questions for any filesystem experts are:
Is there a way to adjust the existing md partitions to get the right alignment for 4k sectors without having to do a file-oriented copy to new partitions? A resize + a dd copy to shift the position might be feasible time-wise if that would work.
I think so. Your partition starts at sector 63, you need anything divisible by 8, so: - 64 is my expectation, - 56 is a fallback solution if the partition does not fit on the disk with 64 sector offset - 2048 would be perfect (1M alignment is currently preferred by Centos 6 and many other OSs)
To be on the safe side, take the disk out of the array (mdadm -f /dev/md0 /dev/sdX1 ; mdadm -r /dev/md0 /dev/sdX1) and clear superblock using mdadm --zero-superblock /dev/sdX1.
Then repartition the disk using fdisk using the following commands: fdisk /dev/sdX u -- display units are sectors c -- no DOS compatibility (== no cyllinder rounding, you definitely want that) o -- new dos partition table n -- new partition p -- primary 1 -- partition 1 64 -- starting offset 1465144065 -- exact size here, because (just to be on the safe side) you do not want to have a larger partition on a rescue disk than on a base disk. Your partition sdh1 has 732572001 1k-blocks, as you wrote in one e-mail, multiply this by 2 (sectors) add 64, (starting offset) subtract 1 because the offset is inclusive. You get 2*732572001+64-1=1465144065. If fdisk complains that this is too much then offset 64 cannot be used and you need to repeat the procedure using offset 56 (don't forget to recalculate ending sector). t -- type fd -- linux raid autodetect w
mdadm -a /dev/mdX /dev/sdX1
And everything should be fine.
Is it worth converting to ext4?
I don't know.
Is there a difference between doing this on 5.6 or 6.x?
Yes, Centos 6 by default aligns partitions on the disk automatically on 1MiB (2048sectors) boundaries. C6 LVM also aligns lv's on 1MiB boundaries relative to the pv start. Finally md in Centos 6 uses 512KiB chunks and aligns data on this boundary (default md superblock in Centos 6 Installer is 1.1 so it is on beginning of the partition) so it is also OK.
If I start over from scratch with 6.x, will the partitioning tools automatically align for 4k sector drives (with/without lvm?)?
Yes. But I always check that to be sure :)
Andrzej