how to re-align data offset

[张柏年 <zhangbonian17@xxxxxxx>]

The backing device /dev/md0 was a raid 0 array with 2 disks and 64k stripe size. The bcache device was created like this:

sudo make-bcache -B /dev/md0

I have just learned from the bcache kernel document that data-offset shoud be provided for data alignment, if the backing device is an array. Is there any way to correct this? 
ps: /dev/bcache0 has already been formated as btrfs

Thanks,
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