Re: HEADS UP - Another media change for HAMMER

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:Would this be possible to convert after time of creation?  e.g. /var is
:one filesystem, but then 6 months later you realize you only need /var/db
:- can /var/db then be "filesystemized"?

    No, that won't work.  For all intents and purposes they would be two
    different filesystems, simply sharing the same storage.

:>From a user interface point of view, I'd rather people didn't have to
:second-guess their file system layout just to take advantage of HAMMER
:features down the road.

    The show-stopper here is going to be in the implemention of the
    replication feature.  To truely replicate a filesystem the inode numbers
    must also be replicated.  It isn't possible to replicate the inode
    numbers without creating collisions unless you create a dedicated
    filesystem for the replication target (so there are no collisions). 

    This feature would allow one to create a dedicated filesystem inside
    another filesystem without having to partition or repartition the
    underlying media.  However, any data you wish to transport from one
    to the other still must be copied.

    Theoretically I could build an ioctl() which deletes and re-inserts
    the B-Tree elements to convert a directory tree, but realistically
    speaking it may impose too much of a burden of complexity on an
    already complex filesystem to be worth doing.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>