On 07/25/2011 10:10 AM, Les Mikesell wrote:
I've mentioned this problem before but put off doing anything about it and maybe now someone can suggest the best solution.
I have a 3-member RAID1 set where one of the members is periodically swapped and rotated offsite. The filesystem contains a backuppc archive which has millions of hardlinks that make it impractical to copy with a file-oriented approach. The current filesystem is ext3 with one partition that uses the entire disk capacity (no lvm). It works as is, but...
I'd like to use a laptop size drive for the swapped member and the only ones available that match the size have 4k sectors. I have swappable, trayless SATA bays available for both drive sizes. The problem is that with the current partition layout, the drive with 4k sectors takes more than a day to re-sync even though on read access the speed is a match for the full sized drives that sync in a few hours.
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.
Is it worth converting to ext4?
Is there a difference between doing this on 5.6 or 6.x?
If I start over from scratch with 6.x, will the partitioning tools automatically align for 4k sector drives (with/without lvm?)?
For LVM's see the --dataalignment and --dataalignmentoffset options. For md devices, my understanding is that the raid superblock is at the end of the partition, so the data is aligned with wherever the partition starts. I verified this using: hexdump /dev/md1 | head -6 hexdump /dev/sda4 | head -6
Nataraj