Dump time issues

[Kevin Oberman]

On Sat, Nov 1, 2014 at 11:47 AM, Kevin Oberman <rkoberman at gmail.com> wrote

> 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 re-installing.
>
> 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
> sense.
>

Memo to self: Don't type stupid responses while watching football games!
Enabling/disabling soft updates journaling requires unmounting the file
system, and re-mounting after the change. In the case of root (or a single
file system), it would require a reboot. A bit too intrusive for many
cases.

Why do I realize these things a few seconds AFTER hitting "Send"?
--
R. Kevin Oberman, Network Engineer, Retired
E-mail: rkoberman at gmail.com