From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Hill Subject: Re: Safe disk replace Date: Wed, 5 Sep 2012 21:32:03 +0100 Message-ID: <20120905203203.GA4391@cthulhu.home.robinhill.me.uk> References: <20120904041447.GB14445@onthe.net.au> <5045D7D9.9000108@hesbynett.no> <20120904153342.GA26999@cthulhu.home.robinhill.me.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="UlVJffcvxoiEqYs2" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids --UlVJffcvxoiEqYs2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed Sep 05, 2012 at 03:35:29PM -0400, John Drescher wrote: > On Wed, Sep 5, 2012 at 10:25 AM, John Drescher wro= te: > >> I'm currently upgrading my RAID-6 arrays via hot-replacement. The > >> process I followed (to replace device YYY in array mdXX) is: > >> - add the new disk to the array as a spare > >> - echo want_replacement > /sys/block/mdXX/md/dev-YYY/state > >> > >> That kicks off the recovery (a straight disk-to-disk copy from YYY to > >> the new disk). After the rebuild is complete, YYY gets failed in the > >> array, so can be safely removed: > >> - mdadm -r /dev/mdXX /dev/mdYYY > >> > > > > Thanks for the info. I wanted this feature for years at work.. > > > > I am testing this now on my test box. Here I have 13 x 250GB SATA 1 > > drives. Yes these are 8+ years old.. > > > > md1 : active raid6 sda2[13](R) sdk2[17] sdj2[18] sdf2[16] sdm2[19] > > sdl2[14] sdi2[12] sdg2[15] sde2[5] sdd2[4] sdh2[21] sdb2[20] sdc2[1] > > 2431477760 blocks super 1.2 level 6, 512k chunk, algorithm 2 > > [12/12] [UUUUUUUUUUUU] > > [>....................] recovery =3D 3.4% (8401408/243147776) > > finish=3D75.9min speed=3D51540K/sec > > > > > > Speeds are faster than failing a drive but I would do this more for > > the lower chance of failure more than the improved performance: > > > > md1 : active raid6 sdk2[17] sdj2[18] sdf2[16] sdm2[19] sdl2[14] > > sdi2[12] sdg2[15] sde2[5] sdd2[4] sdh2[21] sdb2[20] sdc2[1] > > 2431477760 blocks super 1.2 level 6, 512k chunk, algorithm 2 > > [12/11] [_UUUUUUUUUUU] > > [>....................] recovery =3D 1.2% (3134952/243147776) > > finish=3D100.1min speed=3D39954K/sec > > >=20 > I found something interesting. I issued want_replacement without spares. >=20 > localhost md # echo want_replacement > dev-sdd2/state > localhost md # cat /proc/mdstat > Personalities : [raid1] [raid10] [raid6] [raid5] [raid4] [raid0] > [linear] [multipath] > md0 : active raid1 sda1[10](S) sdj1[0] sdk1[2] sdf1[11](S) sdb1[12](S) > sdg1[9] sdh1[8] sdl1[7] sdm1[6] sde1[5] sdd1[4] sdi1[3] sdc1[1] > 1048512 blocks [10/10] [UUUUUUUUUU] >=20 > md1 : active raid6 sdb2[20] sdk2[17] sda2[13] sdj2[18] sdf2[16] > sdm2[19] sdl2[14] sdi2[12] sdg2[15] sde2[5] sdd2[4] sdh2[21] > sdc2[1](F) > 2431477760 blocks super 1.2 level 6, 512k chunk, algorithm 2 > [12/11] [UUUUUUUUUUUU] > > Then I added the failed disk from a previous round as a spare. >=20 > localhost md # mdadm --manage /dev/md1 --remove /dev/sdc2 > mdadm: hot removed /dev/sdc2 from /dev/md1 > localhost md # mdadm --zero-superblock /dev/sdc2 > localhost md # mdadm --manage /dev/md1 --add /dev/sdc2 > mdadm: added /dev/sdc2 >=20 > localhost md # cat /proc/mdstat > Personalities : [raid1] [raid10] [raid6] [raid5] [raid4] [raid0] > [linear] [multipath] > md0 : active raid1 sda1[10](S) sdj1[0] sdk1[2] sdf1[11](S) sdb1[12](S) > sdg1[9] sdh1[8] sdl1[7] sdm1[6] sde1[5] sdd1[4] sdi1[3] sdc1[1] > 1048512 blocks [10/10] [UUUUUUUUUU] >=20 > md1 : active raid6 sdc2[22](R) sdb2[20] sdk2[17] sda2[13] sdj2[18] > sdf2[16] sdm2[19] sdl2[14] sdi2[12] sdg2[15] sde2[5] sdd2[4] sdh2[21] > 2431477760 blocks super 1.2 level 6, 512k chunk, algorithm 2 > [12/11] [UUUUUUUUUUUU] > [>....................] recovery =3D 0.6% (1592256/243147776) > finish=3D119.2min speed=3D33746K/sec >=20 >=20 > Now its taking much longer and it says 12/11 instead of 12/12. >=20 The problem's actually at the point it finishes the recovery. When it fails the replaced disk, it treats it as a failure of an in-array disk. You get the failure email and the array shows as degraded, even though it has the full number of working devices. Your 12/11 would have shown even before you started doing the second replacement. It doesn't seem to cause any problems in use though, and it gets corrected after a reboot. Cheers, Robin --=20 ___ =20 ( ' } | Robin Hill | / / ) | Little Jim says .... | // !! | "He fallen in de water !!" | --UlVJffcvxoiEqYs2 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iEYEARECAAYFAlBHtsIACgkQShxCyD40xBIVyQCg3EdJDkEMvMkQSItbjv9vCU4v uc0Aniai8jZfmA8YxUmaFCBUaJq/GBDc =DB78 -----END PGP SIGNATURE----- --UlVJffcvxoiEqYs2--