chattr

[Michael O'Donnell]

I'd be surprised if dd was anybody's first choice as a
backup utility, but the approach in question (copying
all bits from one device to another) does in fact
work very nicely, resulting in an EXACT copy of the
filesystem in question, unallocated blocks and all.

And there's no requirement that you only copy
to a partition of the same size; the transferred
filesystem carries its own size indication with it.
You can dd a 50Mb filesystem into a 100Mb partition
without any trouble whatsoever, other than the
resultant filesystem will only describe 50Mb worth
of storage, so the remainder of the 100Mb partition
will not be "reachable" because the metadata in the
copied filesystem will not refer to it.  Of course,
trying to copy a 100Mb filesystem to a 50Mb partition
is only rarely successful...  ;->