Why is there no JFS?

Terry Lambert tlambert2 at mindspring.com
Fri Sep 24 08:53:24 PDT 2004

Michael Sierchio wrote:
> Darren Pilgrim wrote:
> >> Soft updates are disable on / by default because of the chicken
> >> and egg problem of runing tunefs on /.
> >
> > If that's the problem, then why doesn't sysinstall enable it by default
> > when partitioning for a new install?
> You can certainly change the options in sysinstall to force Softupdates
> on /
> In general, there's little to be gained from it -- on most systems, / is
> essentially a read-only filesystem, with very little metadata changed except
> for atime.
> BTW, IIRC you can certainly 'tunefs -n enable /' while in single-user mode.

If it's mounted read-only, which requires no other mounts, then you
can do it.

I believe the reason it's not "on" in sysinstall is that sysinstall
tries to mount things async on the initial install, so that doing
things like unpacking ports doesn't take forever.  If it fails, you
can just restart, and having to do that a couple of times is still
faster than waiting for ordered metadata.

The technical reason that it doesn't do it is that the mount update
is not logically an "unmount without destroying vnodes(inodes) in
core, with a remount with the new options".  The main reason for
that is that the dependencies go all the way to the buffer cache,
and the backing vnode (e.g. the "raw" device) that's mounted does
not necessarily get its buffers flushed.  Basically, you'd have to
put a little more work into the "mount update" code.

This was discussed a long time ago on -arch, when soft updates
first came into FreeBSD, and then again every 18 months or so,
ever after.  See Kirk's postings on the subject, if you don't
want to take mine for it.

-- Terry

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