From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: mdadm / RAID, a few questions Date: Sat, 30 Oct 2010 07:44:08 +1100 Message-ID: <20101030074408.05392452@notabene> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mathias =?UTF-8?B?QnVyw6lu?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Fri, 29 Oct 2010 15:18:09 +0100 Mathias Bur=C3=A9n wrote: > Question 3: Before I created this RAID5 array I did a quick RAID0 tes= t > array just for fun, using 2 full devices (not partitions). Now I have > this: >=20 > mdadm --examine --verbose --scan > ARRAY /dev/md/raid0-test level=3Draid0 metadata=3D1.2 num-devices=3D2 > UUID=3Db84cc081:1ae27b49:d5ae466c:377ba300 name=3Dion:raid0-test > devices=3D/dev/sdf,/dev/sdb > ARRAY /dev/md/0 level=3Draid5 metadata=3D1.2 num-devices=3D6 > UUID=3De6595c64:b3ae90b3:f01133ac:3f402d20 name=3Dion:0 > devices=3D/dev/sdg1,/dev/sdf1,/dev/sde1,/dev/sdd1,/dev/sdc1,/dev/s= db1 >=20 > Is it safe to erase the raid0-test superblocks on device /dev/sdb and > /dev/sdc or will it interfere with my RAID5 array (which is lying on > top of partitions) ? It should be safe to mdadm --zero-superblock /dev/sdf /dev/sdb As you have 1.2 metadata, that info will be 4K from the start of the de= vice. Depending on how you partitioned the devices, that is either in dead sp= ace between the partition table and the first partition, or it is in dead s= pace in the first partition just before the md metadata. So the old metadata is still visible, creating the new arrays clearly d= idn't over-write it, so they don't really care what is there... That statement isn't 100% general. A block in the data area of the new = array could be unchanged by creating an array, yet changing it could still co= rrupt parity. However you can be certain that the metadata for a whole-devic= e array does not lie in the data area for a partitioned array of the same metadata type. NeilBrown -- 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