Problems with dump and restore

[Andrew Hamilton-Wright]

Hi Roland -- thanks for the suggestions.


On Tue, 12 Aug 2014, Roland Smith wrote:

> On Tue, Aug 12, 2014 at 01:07:06PM -0300, Andrew Hamilton-Wright wrote:
>
    [ ... condensed ... ]

>> These were created using snapshots, so the level 0 was created via
>>  	dump 0uLCf 32 - /usr
>> and higher level dumps were created similarly.
>
> In 2011, a problem was found with snapshots in combination with soft
> updates *and* journaling (SU+J) hanging the machine. At that time the
> recommendation was to switch off journaling.
> According to https://wiki.freebsd.org/NewFAQs:
>
>    If you want to use snapshot (dump -L) then disable the soft updates
>    journal for that filesystem.
>
> This bug was fixed toward the end of 2011;
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=160662
>
> Personally I make dumps *only* from filesystems that are unmounted or mounted
> read-only, so never from a “live” filesystem, just to be on the safe side.

I had forgotten about the soft update issue.  I am not sure that that
is related, as the machine is running 10.0 and the level 0 dump was
created in July, but it is definitely worth lowering the complexity
of the problem.  I will ensure that soft updates are off before
dumping in the future.



> This is mentioned in the restore's manpage;
>
>     expected next file <inumber>, got <inumber>
>             A file that was not listed in the directory showed up.  This can
>             occur when using a dump created on an active file system.

True, but my understanding of snapshots is that it is supposed to
eliminate exactly this problem, no?



>> Some questions then:
>> - is anyone else using dump/restore as their main backup method?
>
> Yes, operating system filesystems like /, /usr and /var, which can contain
> flags and hard links and such. These filesystem's aren't all that big, so
> dumps are relatively quick.

What options are you using?  Are you using dumplevels?


>>    Are you using snapshots?
>
> No, because of the aforementioned bug that surfaced in 2011.
>
>>  If so, have you seen anything like this when running restore?
>
> I've had hangs and corrupted dumps when dumping live filesystems.

Good to know.


>> - is there any means of validating the dump file, other than the -N
>>    option (which returns no warnings on any of these files)?
>
> Not that I know of. I generally make and verify checksums when copying dumps
> to other machines or external harddrives.

Yes -- I suppose I have gotten lazy in that regard.


>> - does anyone have any advice that may help determine what may have
>>    gone wrong?
>
> Try using restore's “degraded” mode (using the ‘-D’ option) and use the ‘-y’
> option.

I have started that running on a scratch device, and will report back with
results.

Andrew.