From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Hill Subject: Re: Creating new raid5 or 6 with --assume-clean Date: Mon, 2 Dec 2013 08:48:59 +0000 Message-ID: <20131202084859.GA26327@cthulhu.home.robinhill.me.uk> References: <20131202030707.GB19621@animx.eu.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="HcAYCG3uE/tztfnV" Return-path: Content-Disposition: inline In-Reply-To: <20131202030707.GB19621@animx.eu.org> Sender: linux-raid-owner@vger.kernel.org To: Wakko Warner Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --HcAYCG3uE/tztfnV Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun Dec 01, 2013 at 10:07:07PM -0500, Wakko Warner wrote: > This is a general question, but I'll give a specific. >=20 > If I create an array with assume clean and proceed to write to the device, > what happens with the parity? >=20 > EX: > mdadm -C /dev/md0 -n 4 -l 6 -e 1.0 -b internal -c 128 --assume-clean \ > sdc2 sdd2 sdf2 sde2 >=20 > Then: > dd if=3D/dev/zero of=3D/dev/md0 bs=3D1M >=20 > When it finishes, will all the parity blocks be correct for raid 5 and > raid6? >=20 > Would changing md/stripe_cache_size up/down make a difference to the > parities? >=20 Doing that specifically should result in all parity being correct, yes. Providing the writes are not going to a single disk in a stripe (in which case read-modify-write may be used to update the parity rather than a full stripe read and parity recalculation) then any write should result in the parity for that stripe being written correctly. I think RMW is only used in RAID5 currently though. Changing the stripe cache size won't affect the parity calculation at all (except in terms of performance/throughput). Regards, Robin --=20 ___ =20 ( ' } | Robin Hill | / / ) | Little Jim says .... | // !! | "He fallen in de water !!" | --HcAYCG3uE/tztfnV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlKcSXsACgkQShxCyD40xBIBcQCfYz0BeYTFJSgKxxwgGmgBxrVv atsAni2YOw5wK/Sq406Qf2LVtQaE48ZH =lKF3 -----END PGP SIGNATURE----- --HcAYCG3uE/tztfnV--