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Date:      Tue, 03 Oct 2017 10:43:12 +0200
From:      Harald Schmalzbauer <h.schmalzbauer@omnilan.de>
To:        Andriy Gapon <avg@freebsd.org>
Cc:        freebsd-stable@freebsd.org
Subject:   Re: panic: Solaris(panic): blkptr invalid CHECKSUM1
Message-ID:  <59D34DA0.802@omnilan.de>
In-Reply-To: <59D28550.3070700@omnilan.de>
References:  <59CFC6A6.6030600@omnilan.de> <59CFD37A.8080009@omnilan.de> <59D00EE5.7090701@omnilan.de> <493e3eec-53c6-3846-0386-d5d7f4756b11@FreeBSD.org> <59D28550.3070700@omnilan.de>

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 Bez=C3=BCglich Harry Schmalzbauer's Nachricht vom 02.10.2017 20:28 (loca=
ltime):
> Bez=C3=BCglich Andriy Gapon's Nachricht vom 02.10.2017 13:49 (localtime=
):
>> On 01/10/2017 00:38, Harry Schmalzbauer wrote:
>>> Now my striped mirror has all 4 devices healthy available, but all
>>> datasets seem to be lost.
>>> No problem for 450G (99,9_%), but there's a 80M dataset which I'm rea=
lly
>>> missing :-(
>> If it's not too late now, you may try to experiment with an "unwind" /=
 "extreme
>> unwind" import using -F -n / -X -n.  Or manually specifying a txg numb=
er for
>> import (in read-only mode).
> Thanks for your reply!
>
> I had dumped one of each mirror's drive and attaching it as memory disk=

> works as intended.
> So "zfs import" offers me the corrupt backup (on the host with a alread=
y
> recreated pool).
>
> Unfortunately my knowledge about ZFS internals (transaction group numbe=
r
> relations to (=C3=BC)uberblocks) doesn't allow me to follow your hint.
>
> How can I determine the last txg#, resp. the ones before the last?
> I guess 'zpool import -t' is the tool/parameter to use.
> ZFS has wonderful documentation, but although this was a perfect reason=

> to start learning the details about my beloved ZFS, I don't have the
> time to.
>
> Is there a zdb(8) aequivalent of 'zpool import -t', so I can issue the
> zdb check, wich doesn't crash the kernel but only zdb(8)?
>
> For regular 'zpool import', 'zdb -ce' seems to be such a synonym. At
> least the crash report is identical, see my reply to Scott Bennett's po=
st..

Made some progress.
Unfortunately the zpool(8) man page doesn't mention some available
options for the 'import' command.
-T was the important one for me some days ago...
Utilizing internet search engines would have discovered -T, but I
haven't tried...

This post describes the -T (-t for zdb) option very well:
https://lists.freebsd.org/pipermail/freebsd-hackers/2013-July/043131.html=



After attaching the dumps from two of the 4 drives as memory disk,
'zpool import' offers me:
   pool: cetusPsys
     id: 13207378952432032998
  state: DEGRADED
 status: The pool was last accessed by another system.
 action: The pool can be imported despite missing or damaged devices.  Th=
e
        fault tolerance of the pool may be compromised if imported.
   see: http://illumos.org/msg/ZFS-8000-EY
 config:

        cetusPsys                DEGRADED
          mirror-0               DEGRADED
            8178308212021996317  UNAVAIL  cannot open
            md3                  ONLINE
          mirror-1               DEGRADED
            md2p5                ONLINE
            4036286347185017167  UNAVAIL  cannot open

With 'zdb -lu /dev/md3' I picked a TXGid.

The following doesn't panic the kernel:
 zpool import -o readonly=3Don -f -R /net -F -X -n -T 3757541
13207378952432032998 cetusPalt

But:
As soon as I don't tell test-run (not specifying -n), it fails with:
cannot import 'cetusPsys': one or more devices is currently unavailable

I'm clueless again :-(
Is it impossible to import degraded pools in general, or only together
with "-X -T"?

Any tricks to convince zpool import to ignore the missing devices?
I dumped only 2 of 4 disks, the physical disks are in usage.
But people made me hope I have chances to recover data :-) Seems -T had
really offered a way to do that, but I wasn't aware of it some days ago,
so I only have these two tumps, but all data needed should be available
=E2=80=93 I thought...

Thanks,

-harry



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