I would like to see full logging and journaling added to ext2
before we allow such a scheme. ... Then you can add hacks the
filesystem specific code to allow for growing a filesystem...
HP/UX has a logical volume facility which is roughly what you
describe; it also has a VxFS journalling filesystem, both of which
could be cloned for Linux's use. Maybe Remy or Tytso has some
ideas...
-- KTK