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Date:      Mon, 23 Nov 2009 19:02:19 -0800
From:      "Mahlon E. Smith" <mahlon@martini.nu>
To:        Derrick Ryalls <ryallsd@gmail.com>
Cc:        Steve Polyack <korvus@comcast.net>, FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   Re: ZFS disk replacement questions
Message-ID:  <20091124030219.GZ23504@martini.nu>
In-Reply-To: <d5eb95fc0911031132g264182c9qf1c4d51bb1ea2086@mail.gmail.com>
References:  <d5eb95fc0911030937n15bc2c9h73866ca6c7788216@mail.gmail.com> <4AF07493.7050208@comcast.net> <d5eb95fc0911031132g264182c9qf1c4d51bb1ea2086@mail.gmail.com>

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On Tue, Nov 03, 2009, Derrick Ryalls wrote:
> On Tue, Nov 3, 2009 at 10:21 AM, Steve Polyack <korvus@comcast.net> wrote:
> > Derrick Ryalls wrote:
> >>
> >> 1) In the event of a disk failure, how do I trace back the name such
> >> as adX to a physical drive in the enclosure? =A0Is there a way to take
> >> the drive offline then use atacontrol to spin it down or something so
> >> it is easy to identify?
> >>
> >
> > In my opinion you are best off using glabel(8) to give names to the dis=
ks.
> > =A0This way you can name them in a way that makes sense to you. =A0Addi=
tionally,
> > when you create the ZFS pool you will use the glabel'd names. =A0This m=
eans
> > that the pool will still come up properly if something causes your devi=
ces
> > to be numbered differently (i.e. a drive dies and you happen to reboot =
the
> > system).
>=20
> I believe ZFS does this automatically.  Supposedly, if you take a
> working set of RAIDZ drives from one machine and put it in another,
> ZFS will figure out the drives since they get labelled by ZFS
> internally.  My question concerns how to identify the physical disk in
> question based on the adX or glabel name?  Different name in software
> is fine, but if the drive fails I want to make sure I pull the correct
> drive.



This is only true if the metadata on the drives is re-read -- if your
pool loses a drive and the device numbers shuffle, your pool will be
FAILED on the next boot.

You can, however, force the metadata to be re-read via a 'zfs export
POOL', and a subsequent 'zfs import POOL'.=20

However, using glabel avoid that step entirely, as ZFS will always see
the 'right' devices in the right places, regardless of where they are
physically.

-Mahlon

--
Mahlon E. Smith =20
http://www.martini.nu/contact.html

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