Hi, When a 4Kn disk is added to an mdadm array with sector size 512, its sector size changes to 4096 to accommodate the new disk. Here's an example: ``` truncate -s 1G /tmp/loop512a truncate -s 1G /tmp/loop512b truncate -s 1G /tmp/loop512c truncate -s 1G /tmp/loop4Ka losetup --sector-size 512 --direct-io=on /dev/loop0 /tmp/loop512a losetup --sector-size 512 --direct-io=on /dev/loop1 /tmp/loop512b losetup --sector-size 512 --direct-io=on /dev/loop2 /tmp/loop512c losetup --sector-size 4096 --direct-io=on /dev/loop3 /tmp/loop4Ka mdadm --create /dev/md2 --level=5 --raid-devices=3 /dev/loop[0-2] # blockdev returns 512 blockdev --getss /dev/md2 mdadm /dev/md2 -a /dev/loop3 mdadm /dev/md2 -f /dev/loop2 # blockdev still returns 512 blockdev --getss /dev/md2 mdadm -S /dev/md2 mdadm -A /dev/md2 /dev/loop0 /dev/loop1 /dev/loop3 # blockdev now returns 4096 blockdev --getss /dev/md2 ``` This breaks filesystems like XFS, with new mounts failing with: `mount: /mnt: mount(2) system call failed: Function not implemented.` Shouldn't the user be warned when this can happen? Cheers, Filipe
