Funny how the answer is obvious once you ask. I noticed the "Data Offset" was 2048 sectors. On the newly-created md, it was 16 sectors, I think because it was a device mapper overlay and not a real block device. I found this page: http://www.thomas-krenn.com/en/wiki/Linux_Software_RAID Got the mdadm development version that allows setting data offset. 724 parallel truncate -s4000G overlay-{/} ::: $DEVICES 725 parallel 'size=$(blockdev --getsize {}); loop=$(losetup -f --show -- overlay-{/}); echo 0 $size snapshot {} $loop P 8 | dmsetup create {/}' ::: $DEVICES 726 cat /proc/mdstat 727 mdadm -S /dev/md127 728 ~/src/mdadm-40c9a66/mdadm --create /dev/md127 --data-offset=1024 -v -l 0 -n 4 $OVERLAYS That fixed it up (data offset is in k, not sectors). Cheers. -- http://www.subspacefield.org/~travis/ Remediating... LIKE A BOSS
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