a new way to hang 7.0

Matthew Dillon dillon at apollo.backplane.com
Thu Jan 3 15:44:30 PST 2008

:> > I wonder, if this is also a problem on DragonFlyBSD...
:> Since Dragonfly is FreeBSD 4 + some stuff it is unlikely that it even
:> supports UFS snapshots.
:Yes, you are right. I confused the -L with the -C option...
:	-mi

    Well, that description of DragonFly isn't really accurate any more,
    we're about as close to FreeBSD 4 as FreeBSD 7 is.... meaning, not
    really all that close any more, except for the poor interrupt routing

    I froze all the softupdates work in DragonFly prior to the snapshot
    code, and have not performed or allowed any new softupdates work to
    be ported over since then, only bug fixes.  As much as I like the concept
    of softupdates, its been a huge source of bugs in the system ever since
    it was first introduced.  The snapshot code scares me, frankly.  I
    also removed most of the buffer cache hacks related to both it and the
    background writing code long ago... those scared me too.  I kept the
    b_dep concept and implemented the per-buffer b_ops as Kirk (or someone)
    suggested in their comments, though, because HAMMER needs those features.

    DragonFly has a new filesystem called HAMMER in the works which should
    become production ready in a few months.  All primary operations work now
    so it is very real, but major pieces still need to be written and others
    need to be rewritten and stabilized.  It's in pre-alpha state now and
    will be early-alpha by the DFly 2.0 release later this month.  It should
    be in a state that can be ported without having to play constant catchup
    in maybe 2-3 months.  This filesystem has full historical capabilities...
    you don't even have to make snapshots per say, just sync, and you can get
    at any data as-of any point in the past with a simple @@<timestamp>
    file/directory name extension.

    In anycase, my expectation is that HAMMER will replace UFS as our default
    by the end of this year.  Once it gets more polished I don't expect it
    to be all that difficult to port.  You can see the current state of the
    work at:  http://www.dragonflybsd.org/cvsweb/src/sys/vfs/hammer/

    I should have done this years ago.  Ah well, I'm doing it now.


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