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Date:      Tue, 29 Jan 2013 15:52:50 +0100
From:      Fabian Keil <freebsd-listen@fabiankeil.de>
To:        Dan Nelson <dnelson@allantgroup.com>
Cc:        Peter Jeremy <peter@rulingia.com>, current@freebsd.org, fs@freebsd.org
Subject:   Re: Zpool surgery
Message-ID:  <20130129155250.29d8f764@fabiankeil.de>
In-Reply-To: <20130128214111.GA14888@dan.emsphone.com>
References:  <20130127103612.GB38645@acme.spoerlein.net> <1F0546C4D94D4CCE9F6BB4C8FA19FFF2@multiplay.co.uk> <20130127201140.GD29105@server.rulingia.com> <20130128085820.GR35868@acme.spoerlein.net> <20130128205802.1ffab53e@fabiankeil.de> <20130128214111.GA14888@dan.emsphone.com>

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Dan Nelson <dnelson@allantgroup.com> wrote:

> In the last episode (Jan 28), Fabian Keil said:
> > Ulrich Sp=C3=B6rlein <uqs@FreeBSD.org> wrote:
> > > On Mon, 2013-01-28 at 07:11:40 +1100, Peter Jeremy wrote:
> > > > On 2013-Jan-27 14:31:56 -0000, Steven Hartland <killing@multiplay.c=
o.uk> wrote:
> > > > >----- Original Message -----=20
> > > > >From: "Ulrich Sp=C3=B6rlein" <uqs@FreeBSD.org>
> > > > >> I want to transplant my old zpool tank from a 1TB drive to a new
> > > > >> 2TB drive, but *not* use dd(1) or any other cloning mechanism, as
> > > > >> the pool was very full very often and is surely severely
> > > > >> fragmented.
> > > > >
> > > > >Cant you just drop the disk in the original machine, set it as a
> > > > >mirror then once the mirror process has completed break the mirror
> > > > >and remove the 1TB disk.
> > > >=20
> > > > That will replicate any fragmentation as well.  "zfs send | zfs rec=
v"
> > > > is the only (current) way to defragment a ZFS pool.
> >=20
> > It's not obvious to me why "zpool replace" (or doing it manually)
> > would replicate the fragmentation.
>=20
> "zpool replace" essentially adds your new disk as a mirror to the parent
> vdev, then deletes the original disk when the resilver is done.  Since
> mirrors are block-identical copies of each other, the new disk will conta=
in
> an exact copy of the original disk, followed by 1TB of freespace.

Thanks for the explanation.

I was under the impression that zfs mirrors worked at a higher
level than traditional mirrors like gmirror but there seems to
be indeed less magic than I expected.

Fabian

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