From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: RAID6 chunk size change? Date: Mon, 24 Jan 2011 00:52:04 +0500 Message-ID: <20110124005204.71688cc2@natsu> References: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/oYQRnXKf_lfs3WrdtB6hG+U"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mark Knecht Cc: Linux-RAID List-Id: linux-raid.ids --Sig_/oYQRnXKf_lfs3WrdtB6hG+U Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sun, 23 Jan 2011 11:10:40 -0800 Mark Knecht wrote: > On Sun, Jan 23, 2011 at 10:53 AM, Mark Knecht wrot= e: > > Hi, > > =C2=A0 I've got an existing (and well backed up as of a couple of minut= es > > ago) 5-drive RAID6 shown here: > > > > c2stable ~ # mdadm --detail /dev/md7 > > /dev/md7: > > =C2=A0 =C2=A0 =C2=A0 =C2=A0Version : 1.2 > > =C2=A0Creation Time : Sun Jan 16 17:02:24 2011 > > =C2=A0 =C2=A0 Raid Level : raid6 > > =C2=A0 =C2=A0 Array Size : 395387904 (377.07 GiB 404.88 GB) > > =C2=A0Used Dev Size : 131795968 (125.69 GiB 134.96 GB) > > =C2=A0 Raid Devices : 5 > > =C2=A0Total Devices : 5 > > =C2=A0 =C2=A0Persistence : Superblock is persistent > > > > =C2=A0 =C2=A0Update Time : Sun Jan 23 10:25:41 2011 > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0State : clean > > =C2=A0Active Devices : 5 > > Working Devices : 5 > > =C2=A0Failed Devices : 0 > > =C2=A0Spare Devices : 0 > > > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 Layout : left-symmetric > > =C2=A0 =C2=A0 Chunk Size : 512K > > > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 Name : c2stable:7 =C2=A0(local to ho= st c2stable) > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 UUID : ded5e0c6:1a5a73ad:01949557:bb= 4e015a > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 Events : 17 > > > > =C2=A0 =C2=A0Number =C2=A0 Major =C2=A0 Minor =C2=A0 RaidDevice State > > =C2=A0 =C2=A0 =C2=A0 0 =C2=A0 =C2=A0 =C2=A0 8 =C2=A0 =C2=A0 =C2=A0 =C2= =A07 =C2=A0 =C2=A0 =C2=A0 =C2=A00 =C2=A0 =C2=A0 =C2=A0active sync =C2=A0 /d= ev/sda7 > > =C2=A0 =C2=A0 =C2=A0 1 =C2=A0 =C2=A0 =C2=A0 8 =C2=A0 =C2=A0 =C2=A0 23 = =C2=A0 =C2=A0 =C2=A0 =C2=A01 =C2=A0 =C2=A0 =C2=A0active sync =C2=A0 /dev/sd= b7 > > =C2=A0 =C2=A0 =C2=A0 2 =C2=A0 =C2=A0 =C2=A0 8 =C2=A0 =C2=A0 =C2=A0 39 = =C2=A0 =C2=A0 =C2=A0 =C2=A02 =C2=A0 =C2=A0 =C2=A0active sync =C2=A0 /dev/sd= c7 > > =C2=A0 =C2=A0 =C2=A0 3 =C2=A0 =C2=A0 =C2=A0 8 =C2=A0 =C2=A0 =C2=A0 50 = =C2=A0 =C2=A0 =C2=A0 =C2=A03 =C2=A0 =C2=A0 =C2=A0active sync =C2=A0 /dev/sd= d2 > > =C2=A0 =C2=A0 =C2=A0 4 =C2=A0 =C2=A0 =C2=A0 8 =C2=A0 =C2=A0 =C2=A0 66 = =C2=A0 =C2=A0 =C2=A0 =C2=A04 =C2=A0 =C2=A0 =C2=A0active sync =C2=A0 /dev/sd= e2 > > c2stable ~ # > > > > =C2=A0 I would like to change this RAID to a smaller chunk size. (16K f= or > > now) What is the right command to use? > > > > =C2=A0 From Google and the mdadm man pages I'm coming up with something= like: > > > > mdadm --grow /dev/md7 --level=3D6 --chunk=3D16 --backup-file=3D/root/ba= ckup-md7 > > > > Maybe I don't need --level because the level isn't changing? Neither > > is the number of drives. > > > > Thanks in advance, > > Mark > > >=20 > OK, I found a blog of Neil's in which I had read the top but hadn't > gone through the comments: >=20 > http://neil.brown.name/blog/20090817000931 > It seems he answers my question further down in the comments. >=20 > Looks like >=20 > mdadm --grow /dev/md7 --chunk=3D16 I suggest that you reconsider going with 16K, it is a suboptimal chunk size. The older default of 64K seems to be the sweet spot, at least for RAID5/6: http://louwrentius.com/blog/2010/05/linux-raid-level-and-chunk-size-the-ben= chmarks/ --=20 With respect, Roman --Sig_/oYQRnXKf_lfs3WrdtB6hG+U Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iEYEARECAAYFAk08huQACgkQTLKSvz+PZwj86wCfaLb+4rl0vQPuji1CPt52cMl6 OSgAnR6th65lIh/LwH9jHAVRb3BSyFWM =WuNZ -----END PGP SIGNATURE----- --Sig_/oYQRnXKf_lfs3WrdtB6hG+U--