From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Recovering from an URE on a RAID5 rebuild/resize Date: Fri, 25 Jan 2013 17:14:59 +0600 Message-ID: <20130125171459.5f855c92@natsu> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/lPZH7xqNy43SaduMbKHlRA_"; protocol="application/pgp-signature" Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/lPZH7xqNy43SaduMbKHlRA_ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Hello, Recently there has been some talk on this list, about probability of seeing= an URE during a RAID5 rebuild on modern large (e.g. 2TB) drives. I would like to ask for some advice of what would be the best way to proceed when such an URE is encountered. This is mostly theoretical, no real situat= ion at hand at the moment. As I understand, a RAID5 that is being resized or rebuilt, has no redundanc= y; it is essentially as reliable as a RAID0 of total members-1, or even less. So on an unreadable sector that mdadm needs to read (because it has no redundancy to recover it from), mdadm will: - mark the corresponding array member as "failed"; - mark the one that was being rebuilt/resized onto as "spare"; - and the whole array as down and "not enough members to start the array". Let's assume only a couple of sectors on that member were unreadable, and t= hen their readability was restored (either by drive replacement or by overwriti= ng them to making the drive remap), and I would be okay with losing data that = was in those sectors. What would be the best way to proceed from there? --=20 With respect, Roman ~~~~~~~~~~~~~~~~~~~~~~~~~~~ "Stallman had a printer, with code he could not see. So he began to tinker, and set the software free." --Sig_/lPZH7xqNy43SaduMbKHlRA_ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlECaTMACgkQTLKSvz+PZwg4gACZAb9s/eqkTOLcov4NquXJ7Tca Ci0An0d02YHvqqNYYzxeG/MilgggSOx/ =kng8 -----END PGP SIGNATURE----- --Sig_/lPZH7xqNy43SaduMbKHlRA_--