From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zoltan Szecsei Subject: Re: Confusion with setting up new RAID6 with mdadm Date: Tue, 16 Nov 2010 08:48:59 +0200 Message-ID: <4CE2295B.8050403@geograph.co.za> References: <4CE00206.4000301@geograph.co.za> <20101115091326.42b38b84@notabene.brown> <4CE1758C.5080008@geograph.co.za> <20101116065325.6dd5e8cf@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20101116065325.6dd5e8cf@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 2010-11-15 21:53, Neil Brown wrote: > On Mon, 15 Nov 2010 20:01:48 +0200 > Zoltan Szecsei wrote: > > =20 >> Hi, >> One last quick question: >> **************************************************** >> I have compiled the following mdadm on my Ubuntu 64 bit 10.04 Deskto= p >> system: >> root@gs0:/home/geograph# uname -a >> Linux gs0 2.6.32-25-generic #45-Ubuntu SMP Sat Oct 16 19:52:42 UTC 2= 010 >> x86_64 GNU/Linux >> root@gs0:/home/geograph# mdadm -V >> mdadm - v3.1.4 - 31st August 2010 >> root@gs0:/home/geograph# >> >> **************************************************** >> I have deleted the partitions on all 8 drives, and done a mdadm -Ss >> >> root@gs0:/home/geograph# fdisk -lu >> >> Disk /dev/sda: 2000.4 GB, 2000398934016 bytes >> 255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sect= ors >> Units =3D sectors of 1 * 512 =3D 512 bytes >> Sector size (logical/physical): 512 bytes / 512 bytes >> I/O size (minimum/optimal): 512 bytes / 512 bytes >> Disk identifier: 0x00000000 >> >> Disk /dev/sda doesn't contain a valid partition table >> >> Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes >> >> ****************************************************** >> Based on the above "assume-clean" comment, plus all the help you guy= s >> have offered, I have just run: >> mdadm --create /dev/md0 --metadata=3D1.2 --auto=3Dmd --assume-clean >> --bitmap=3Dinternal --bitmap-chunk=3D131072 --chunk=3D512 --level=3D= 6 >> --raid-devices=3D8 /dev/sd[abcdefgh] >> >> It took a nano-second to complete! >> >> The man-pages for assume-clean say that "the array pre-existed". Sur= ely >> as I have erased the HDs, and now have no partitions on them, this i= s >> not true? >> Do I need to re-run the above mdadm command, or is it safe to procee= d >> with LVM then mkfs ext4? >> =20 > It is safe to proceed. > =20 Too cool (A for away at last :-) ) Neil: Big thanks to you and the others on this list for all the patienc= e=20 & help you guys have given., Kind regards, Zoltan > The situation is that the two parity block are probably not correct o= n most > (or even any) stripes. But you have no live data on them to protect,= so it > doesn't really matter. > > With the current implementation of RAID6, every time you write, the c= orrect > parity blocks are computed and written. So any live data that is wri= tten > will be accompanies by correct parity blocks to protect it. > > This does *not* apply to RAID5 as it sometimes uses the old parity bl= ock to > compute the new parity block. If the old was wrong, the new will be = wrong > too. > > It is conceivable that one day we might change the raid6 code to perf= orm > similar updates if it ever turns out to be faster to do it that way, = but it > seems unlikely at the moment. > > NeilBrown > > > =20 --=20 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Zoltan Szecsei PrGISc [PGP0031] Geograph (Pty) Ltd. P.O. Box 7, Muizenberg 7950, South Africa. 65 Main Road, Muizenberg 7945 Western Cape, South Africa. 34=B0 6'16.35"S 18=B028'5.62"E Tel: +27-21-7884897 Mobile: +27-83-6004028 =46ax: +27-86-6115323 www.geograph.co.za =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1153 / Virus Database: 424/3258 - Release Date: 11/15/10 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html