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Date:      Wed, 02 Mar 2011 17:28:05 -0600
From:      "James R. Van Artsdalen" <james-freebsd-fs2@jrv.org>
To:        Emil Smolenski <am@raisa.eu.org>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: [ZFS] Booting from zpool created on 4k-sector drive
Message-ID:  <4D6ED285.6010105@jrv.org>
In-Reply-To: <op.vrm32cqdk84lxj@bolt.zol>
References:  <op.vn2iid1qk84lxj@arrow> <4D6AAC9A.4000602@jrv.org>	<op.vrmp2hrck84lxj@bolt.zol>	<AANLkTi=w9_d=2W_-_F62AxenmdBs7rE%2BbVAbmR2e877y@mail.gmail.com> <op.vrm32cqdk84lxj@bolt.zol>

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Emil Smolenski wrote:
> James asks about disk replacement scenario. In this case you cannot
> use device with greater sector size than 2**ashift of the existing
> vdev as replacement:
>
> # diskinfo -v md0 |grep sectorsize
>         512             # sectorsize
> # zpool create test0 md0
> # zdb test0 |grep ashift
>                 ashift=9
> # diskinfo -v md1.nop |grep sectorsize
>         4096            # sectorsize
> # zpool replace test0 md0 md1.nop
> cannot replace md0 with md1.nop: devices have different sector alignment

I was thinking of the capacity of the drive as a problem, not the sector
sizes.  I wrongly thought gnop consumed space on the drive (like
gmirror) and this might make it hard to replace an ashift=12 disk with a
512-byte-sector disk.  But this is not the case.

It might be a good idea now to start using the gnop trick to force
vdev's to use ashift=12 in case disks begin advertising themselvess as
4096-byte-sector.



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