> (read as "at some undefined time in future" and "at undefined
> order"), it may not have hit the disk yet after the change or may
> only hit the disk partially. So you CAN'T recover it. If you write
> metadata synchronously (read "immediatelly"), you can be sure all
> the changed metadata HIT the disk, so potential crash or anything
> is not such disastrous. softdep maintains best of both words - it
> postpones writing the metadata similar way as async does, but writes
> all related metadata together, so that it garantees the state on
> disk is consitent.

"almost guarantees". actually disk itself has write buffers and could
reorder writes. 

> If you really really think async metadata is the way to go, you can
> mount async if you prefer to. IIRC there is no option to write
> only metadata sync on ext2fs under Linux though.
yes. there is sync option only - incredibly slow