From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Data Offset Date: Thu, 24 May 2012 15:20:38 +1000 Message-ID: <20120524152038.1d01b866@notabene.brown> References: <20120510174210.GA2991@lazy.lzy> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/WWEOhC65I8lXj0qDqpeEAO="; protocol="application/pgp-signature" Return-path: In-Reply-To: <20120510174210.GA2991@lazy.lzy> Sender: linux-raid-owner@vger.kernel.org To: Piergiorgio Sartor Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/WWEOhC65I8lXj0qDqpeEAO= Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 10 May 2012 19:42:10 +0200 Piergiorgio Sartor wrote: > Hi, >=20 > after the RAID-5 problem, I just realized that > other RAIDs I have, including a multi RAID-6, > have different data offset for each component. >=20 > This seems to be quite of a problem, in case > "Create" is used to recover an array. >=20 > Obviouly, if a 4 disks RAID-5 has 2 disks with > one offset and 2 with another, it will not be > possible to re-create it (saving the data). I certainly won't be easy. Though if someone did find themselves in that situation it might motivate me to enhance mdadm in some way to make it easi= ly fixable. >=20 > Is there any way to fix/prevent such issue? > Shouldn't "mdadm" make sure all offset are > the same? Or try, at least... I'm not sure. Maybe... With linux-3.5 and mdadm-3.3 (both unreleased) you will probably be able to mdadm --grow --data-offset=3D5M and that will happen. At least for RAID10. Other levels might follow late= r. Should mdadm keep them always the same? The reason that it doesn't is that= I thought that you could change the data offset by removing each device and adding it back as a spare with a new data_offset. Maybe that isn't such a good idea. I suspect that I got a chorus of people all saying "please keep data_offset consistent" - and particular if I received a patch which did that - then I would probably change mdadm accordingly. NeilBrown >=20 > What I noticed is that, adding a disk later, > might cause different offsets. >=20 > Any idea? >=20 > Thanks, >=20 > bye, >=20 --Sig_/WWEOhC65I8lXj0qDqpeEAO= Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBT73FJznsnt1WYoG5AQJv7A/8DsZTSdD2+gMzg7aRAVIW0/XRS247DAsa xgd+wdG7bf+wxM1LqTx4x880V9TDy6ZvvA5/E6pnCYyyfT74ycXb8I5EMT7pbCba INsIckKx5KRdJWWxMVq6APHLDe2FWc3EKLsu4zqVEDFP7xBXut+6H40C9qBJNZes Sln1lb/J3MWE2jONYiXYGXgENPxrRUN/hIZTSkCF2d01v8rtR3BN0idbGgfCeN8r rUmAJO0QQfDf5ddKTCjsFEdORo26OuMccFQm51myC27S9dIZkrM/3BoMDO1pWqwM wo0IXdPUmCsNwdveZ5YTg7tfT1+R9LqrVqEstO7WsL9+DeYtRag7i31isdUEO9PQ XJ+dY588NHwtAklAGCwO1p92+nlumL+7Br033fFFUJxxjlFuquD8hP1UwqT/Eo0J vZRjb8uiqUn4uXAPfAT7pEJy+L/xHb73BVzQizwLGS8RFiEXK2EJ5SOZeDrfR9MU oWNlwqwYN5l/q1cOAP9KJmI6UiAfRLUvj3i6rH5388I4fGkShp9JTpuZmcN1NfB+ RvP5dsAQPX+SPOfPC5Z0PxixubFegdJ8T+HnrKBzjFOPhZ9OhWVJJtaDqO2HE0yD uBkTG+EAamZ0VvmTqZzdI+iHTfnYKscOoqiidlI2hh3MMo9ERNwxSqaDihQBy3dj wSlGRcexJzI= =MQAr -----END PGP SIGNATURE----- --Sig_/WWEOhC65I8lXj0qDqpeEAO=--