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Date:      Tue, 19 Oct 2010 14:03:11 -0700
From:      Freddie Cash <fjwcash@gmail.com>
To:        freebsd-fs@freebsd.org
Subject:   Re: ZFS 'read-only' device / pool scan / import?
Message-ID:  <AANLkTi=DikO4-N8BG4U0WBX-7ypbPkVCR8=vHSaeN3qV@mail.gmail.com>
In-Reply-To: <4CBDFFF6.5080701@digiware.nl>
References:  <AE519076FDEA1259C5DEA689@HexaDeca64.dmpriest.net.uk> <20101019151602.GA61733@icarus.home.lan> <7BEF90D9F4D4CB985F3573C3@HexaDeca64.dmpriest.net.uk> <4CBDFFF6.5080701@digiware.nl>

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On Tue, Oct 19, 2010 at 1:30 PM, Willem Jan Withagen <wjw@digiware.nl> wrot=
e:
> On 2010-10-19 17:30, Karl Pielorz wrote:
>
>> As there is such a large aspect of human error (and controller
>> behaviour), I don't think it's worth digging into any deeper. It's the
>> first pool we've ever "lost" under ZFS, and like I said a combination of
>> the controller collapsing devices, and humans replacing wrong disks,
>> 'twas doomed to fail from the start.
>>
>> We've replaced failed drives on this system before - but never rebooted
>> after a failure, before a replacement - and never replaced the wrong
>> drive :)
>>
>> Definitely a good advert for backups though :)
>
> I'm running my ZFS stuff on a 3ware and an areca controller, and they onc=
e
> in a while forgot their order of disks during booting.
> (the 3ware got fixed by a bios upgrade)
> The areca just keeps reordering no matter how hard you like to tell it
> otherwise.
>
> But GPT really proves useful since reallocation of disks does not result =
in
> a different device in the gpt directory.
>
> eg.:
> =C2=A0pool: zroot
> =C2=A0state: ONLINE
> =C2=A0scrub: none requested
> config:
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0NAME =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 STATE =
=C2=A0 =C2=A0 READ WRITE CKSUM
> =C2=A0 =C2=A0 =C2=A0 =C2=A0zroot =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0ONLINE=
 =C2=A0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0mirror =C2=A0 =C2=A0 =C2=A0 ONLINE =C2=
=A0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0gpt/root4 =C2=A0ONLINE =C2=A0 =
=C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0gpt/root6 =C2=A0ONLINE =C2=A0 =
=C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 0
>
> I could even migrate a disk from the 3ware controller to the std SATA
> interfaces without losing the the gpt-label.

While using labelled devices (be it glabel, gpt label, or whatever)
certainly helps keep things ordered and working.

However, ZFS also labels the devices in the pool.  A simple "zpool
export poolname" followed by a "zpool import poolname" will scan the
metadata on the drives, find all the devices in the pool, re-order
things internally, and carry on.

Back when I started with ZFS, I used unlabelled drives (also on 3Ware
controllers) and made the mistake once of booting with a failed drive
removed.  Pool came up faulted saying all the drives after the missing
one were also faulted.  Thought I lost the whole pool.  However, some
digging online showed the export/import info, and I was able to
continue on without losing any data.

--=20
Freddie Cash
fjwcash@gmail.com



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