From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: Growing 6 HDD RAID5 to 7 HDD RAID5 Date: Wed, 13 Apr 2011 00:22:38 +0600 Message-ID: <20110413002238.3f31bdeb@natsu> References: <20110412231401.5bb9065c@natsu> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/ssZLpGf_7=NkbA6H0UmdzAJ"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mathias =?UTF-8?B?QnVyw6lu?= Cc: Linux-RAID List-Id: linux-raid.ids --Sig_/ssZLpGf_7=NkbA6H0UmdzAJ Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, 12 Apr 2011 18:21:13 +0100 Mathias Bur=C3=A9n wrote: > If I use --layout=3Dpreserve , what impact will that have? > If I preserve the layout, what is the final result of the array > compared to not preserving it? Neil wrote about this on his blog: "It is a very similar process that can now be used to convert a RAID5 to a RAID6. We first change the RAID5 to RAID6 with a non-standard layout that h= as the parity blocks distributed as normal, but the Q blocks all on the last device (a new device). So this is RAID6 using the RAID6 driver, but with a non-RAID6 layout. So we "simply" change the layout and the job is done." http://neil.brown.name/blog/20090817000931 Admittedly it is not completely clear to me what are the long-term downside= s of this layout. As I understand it does fully provide the RAID6-level redundan= cy. Perhaps just the performance will suffer a bit? Maybe someone can explain t= his more. If anything, I think it is safe to use this layout for a while, e.g. in case you don't want to rebuild 'right now'. You can always change the layout to = the traditional one later, by issuing "--grow --layout=3Dnormalise". Or perhaps= if you plan to add another disk soon, you can normalise it on that occasion, a= nd still gain the benefit of only one full reshape. > Will the array have redundancy during the rebuild of the new drive? If you choose --layout=3Dpreserve, your array immediately becomes a RAID6 w= ith one rebuilding drive. So this is the kind of redundancy you will have during that rebuild - tolerance of up to one more (among the "old" drives) failure, in other words, identical to what you currently have with RAID5. --=20 With respect, Roman --Sig_/ssZLpGf_7=NkbA6H0UmdzAJ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEARECAAYFAk2kmG4ACgkQTLKSvz+PZwh+1ACfZ5AlZg/ZQpJ48nC3llGqmPLM J+4Anj2ZdAkR4vXdKG59z9Z2wtm4aRPw =X1gx -----END PGP SIGNATURE----- --Sig_/ssZLpGf_7=NkbA6H0UmdzAJ--