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Date:      Sun, 13 Aug 2017 12:55:25 -0400
From:      Chris Ross <cross+freebsd@distal.com>
To:        Volodymyr Kostyrko <arcade@b1t.name>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: Oh no, what have I done...
Message-ID:  <8EE368A2-D2BA-4E43-8B84-47E8F50B5B1B@distal.com>
In-Reply-To: <1d3771a3-9c3a-1af9-9c48-032a01629630@b1t.name>
References:  <3408A832-BF2E-4525-9EAC-40979BA3555B@distal.com> <20170813000323.GC95431@server.rulingia.com> <5B508AED-4DAC-42E4-8C56-4619C0D1A1C6@distal.com> <035BFBCB-BA43-4568-89E9-8E8DCDFAA8CA@kraus-haus.org> <928F1F16-0777-4D66-BD27-8224DF80363C@distal.com> <06EEEF86-E466-44EA-86F1-866DA32DD92D@kraus-haus.org> <1d3771a3-9c3a-1af9-9c48-032a01629630@b1t.name>

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> On Aug 13, 2017, at 09:54 , Volodymyr Kostyrko <arcade@b1t.name> =
wrote:
>=20
> Paul Kraus wrote:
>=20
>> Using zdb you can examine the TXGs and there is a way to force an =
import to a certain TXG (at least under Illumos there is, I assume the =
FBSD ZFS code is the same). I do not remember the specific procedure, =
but it went by on one of the ZFS mailing lists a few years ago. The goal =
at the time was not to deal with a changed pool configuration but a =
series of writes that corrupted something (possibly due to a feature =
being turned on at a certain point in time). You would lose all data =
written after the TXG you force the import to.
>>=20
>> Looking at the manpages for zpool and zdb, it looks like doing this =
has gotten easier with `zdb -e -F` =E2=80=A6 operate on exported pool =
and rollback TXG until the pool is importable =E2=80=A6 but I=E2=80=99m =
sure there are limits :-)
>=20
> That's -T, it was intentionally left undocumented.
>=20
> /usr/src/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c /starting txg

  Thanks Peter, Paul, Volodymyr, and all.  So I got my pool back online, =
just in a way I don=E2=80=99t like it, so I=E2=80=99m trying to find a =
place I can export (zfs send) the 5+ TB of data.  Disadvantage of having =
my largest data-store machine be the problem machine.  :-)

  But, were I in a state as I was earlier in recent days, and I =
understand the above, I might=E2=80=99ve been able to =E2=80=9Czfs =
import -T=E2=80=9D to a TXG that was before I added the single-drive =
vdev, and it would=E2=80=99ve imported just the working raidz1 and been =
okay?  If any data had been written in the very small time the new vdev =
was added, that would be lost, but I would=E2=80=99ve been fine with =
that.

  And, if I understand correctly, I would=E2=80=99ve used =E2=80=9Czdb=E2=80=
=9D to find out what the TXG that I wanted to refer to was?  Paul, you =
mention using zdb against an exported pool, which of course I didn=E2=80=99=
t have.  Could I have found the old TXG to import from without having an =
export?  Just that that seems to be the gap I=E2=80=99m missing in the =
above.

  But, all is well.  Or at least, 99+% recoverable, it seems.  Thank you =
all for your time and information.  What do rebuild after I find a way =
to back the pool up will be this next weeks problem.

               - Chris

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