From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: question about bitmap for raid6 Date: Tue, 11 Sep 2012 09:07:48 +1000 Message-ID: <20120911090748.59087250@notabene.brown> References: <2CE44BD3DBCF9541909CCB42F11CA39284A4F5@SFO1EXC-MBXP06.nbttech.com> <20120910085035.3fe12f99@notabene.brown> <2CE44BD3DBCF9541909CCB42F11CA39284A942@SFO1EXC-MBXP06.nbttech.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/HF9TqpEz00_uyr_wfAIhN=g"; protocol="application/pgp-signature" Return-path: In-Reply-To: <2CE44BD3DBCF9541909CCB42F11CA39284A942@SFO1EXC-MBXP06.nbttech.com> Sender: linux-raid-owner@vger.kernel.org To: Ming Lei Cc: "linux-raid@vger.kernel.org" List-Id: linux-raid.ids --Sig_/HF9TqpEz00_uyr_wfAIhN=g Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Mon, 10 Sep 2012 16:43:14 +0000 Ming Lei wrote: > Neil, >=20 > How about the other scenario: I plug out a drive and put aside for a whil= e and put it back to the same machine with bitmap enabled for the raid6 arr= ay? Does it do full-recovery or fast resync? If the array has been degraded that whole time, it will do a fast resync. >=20 > I noticed either md superblock or bitmap superblock has events recorded a= nd I guess it may be used to identify the up-to-date drive or the old drive= put back again.=20 Correct. NeilBrown >=20 > Thanks > Ming >=20 > -----Original Message----- > From: NeilBrown [mailto:neilb@suse.de]=20 > Sent: Sunday, September 09, 2012 3:51 PM > To: Ming Lei > Subject: Re: question about bitmap for raid6 >=20 > On Sat, 8 Sep 2012 21:07:46 +0000 Ming Lei wrote: >=20 > > Hi Neil, > >=20 > > We use 2.6.32 in house and most recently we found something bad happen = when we turn on bitmap for raid6 array. Let me ask a question to help me to= understand our situation. > >=20 > > Say I have two hardware identical PCs(name them A and B) running with t= he same linux distribution. Both box has an raid6 array assmeblying 7 drive= s with internal bitmap. If I yank out one drive from PC B to make this driv= e slot empty, and then yank out a drive from PC A and move it to PC B, woul= d md driver force the raid6 array on PC B rebuild(take a long time) or just= do resync(very short time)? What's the condition on bitmap code to check i= f it is really the drive I just pull out from the same machine or it is the= drive pulled out from different machine? > >=20 > > Thanks > > Ming >=20 > PC B would not do anything to drive that you moved from PC A until you ad= d it as a spare. Then it will perform a complete rebuild of the missing de= vice to the new device. It will not do a partial recovery. >=20 > 'md' knows it is a device from a different array because the 'uuid' store= d in the metadata is different. > If you managed to create two arrays on two different PCs which both had t= he same UUID, then you could definitely get strange data corruption happen= ing, but that is very unlikely. >=20 > NeilBrown >=20 > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html --Sig_/HF9TqpEz00_uyr_wfAIhN=g Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBUE5yxDnsnt1WYoG5AQJIuw//UE/zpjcOOqTYLG0KuyHDtSnYf+++zdJv 3qzKDFf7H0CvcXFkkTubuEJgUUetUgSZFXpBYBr5tcoUYsGWRHMYVLFUl8DtIX2K uz4ACpw0G6wuO5GYrrI9viIoRqmzrHyvAE9JF2ZA9QdsKXilo5FvUQfwLznccQgZ YvnS6ULt1OHzEbvqTjLW/SopNe5M/N/cEo2plyfVZnZs/6el7twtksaLLBMHNdTj x6yZsyNgoPCaLY6EwbNpYesy1iFIK7sWuQ8kAbillooWhWAgEPC9jMupTV/jAN/2 W0Jq4in0+KhR3hYyQbT+tR6QIdTr+IJvANsjBPC8EKcQw4oHhO8Razjb7pA7SkaY VgjrhJM6Bm2IkopFg0mRKOAefGVJlOr/ehfmFke9Lhmf2NFYMIX1AU7aCiWy1nQs Y+lAZbVidNiktAeWSgzJpBsIZynMdLpa5OST3/JIHI/pv4z/rbk/tcyx0mijxIuI H7rSk0EYGyxd7oQ8vzU3TSjMwnHUbodBu54eqd1aHOlKZH6sG2BT2i3wn4tWdw0n HprGFt07ZtXCW/Oa3U3p2I/BAznhXaCnmPrMuQOyDWKBiwnhg+yQBBZLtQdYJWAv dRl2OCWlErlYSOdnYk35EobvfaYQmNqHlId4Jqp/HC7ipoiKd6zHtGpw9KN7fulW nqKAFp98oxg= =uR3c -----END PGP SIGNATURE----- --Sig_/HF9TqpEz00_uyr_wfAIhN=g--