I still don't like the idea of btrfs trying to be smarter than a user
who can partition up his system according to
(a) his likes
(b) system or hardware requirements or recommendations
to align the superblock to a specific location.
1MB alignment does not always mean 1MB alignment.
Sector 1 begins at 0x7e00 on x86.
And with the maximum CHS geometry (255/63), partitions begin
at 0x7e00+n*8225280 bytes, so the SB is unlikely to ever be on
a 1048576 boundary.
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