Dump time issues

Kevin Oberman rkoberman at gmail.com
Sat Nov 1 18:47:24 UTC 2014

On Fri, Oct 31, 2014 at 8:10 AM, Chris H <bsd-lists at bsdforge.com> wrote:

> On Tue, 28 Oct 2014 12:20:01 -0700 Adrian Chadd <adrian at freebsd.org> wrote
> > On 27 October 2014 11:09, Kevin Oberman <rkoberman at gmail.com> wrote:
> >
> > >> I'm aware of two issues with SU+J, one of which is annoying and the
> other
> > > is worse.
> > > 1. If the journal is not fully written on power fail or some other
> reason,
> > > you may need to do a full fsck of the volume and the behavior of the
> system
> > > until this is done can be very unpredictable.
> > > 2. You can't safely snapshot the system. This is what 'dump -L' does.
> This
> > > means that some files dumped from a live FS may not be consistent (not
> > > good!) or, if '-L' is used, the system may well hang.
> > >
> > > While I love the fast fsck times (2 or 3 seconds) after a crash, I also
> > > question the default. Still, it may be a preferred choice be used for
> very
> > > large file systems where a full fsck would take a very long time as
> long as
> > > the risks are understood. For these systems, ZFS might be a better
> choice.
> > > These arguments do NOT favor it being the default, IMHO.
> >
> > If people can reproduce SU+J problems then please file bugs. There
> > have been some fixes with the journal handling over the last year or
> > so and I haven't had this problem on -HEAD any longer, but it doesn't
> > mean it's there.
> Problem existed on RELENG_9 as of 1 mos, and 1 wk. ago. I don't
> have any useful output to provide (I simply blew away the system
> && re-installed w/o SU+J).
> --Chris

You should be to deal with that using "tunefs -j disable". Much easier than

Would disabling soft updates journaling, snapshotting, and re-enabling
would work around the issue? I might play with this when I get a chance. If
it works, perhaps tools (mostly dump -L) could check for SU+J and turn it
off for the time to snapshot the file system. I'm just not sure how well
re-enabling works. Certainly some journal data would be lost, but the
snapshot operation should make that irrelevant. I just don't know that I
understand the details of SU+J well enough to know whether this would make
R. Kevin Oberman, Network Engineer, Retired
E-mail: rkoberman at gmail.com

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