a new way to hang 7.0
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...
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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