From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: metadata versions: 0.90 vs 1.2 Date: Wed, 13 Jun 2012 11:31:34 +0200 Message-ID: <4FD85DF6.4000805@hesbynett.no> References: <1339563343.41566.YahooMailClassic@web190003.mail.sg3.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1339563343.41566.YahooMailClassic@web190003.mail.sg3.yahoo.com> Sender: linux-raid-owner@vger.kernel.org To: plug bert Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 13/06/2012 06:55, plug bert wrote: > Hello, > > i noticed this while twiddling with RAID1 arrays... > > On our old CentOS 4.7 box, i can mount a RAID1 array member > independently of the array -- i.e. mount /dev/sdc1 /mountpoint....but > on CentOS 5.x and later i am met with an unknown filesystem: > linux_raid_member error. > > Somebody hinted that this had something to do with the metadata > versions, so i recreated the RAID1 array on CentOS 5.x with the > --metadata=0.90 parameter...and was able to mount the array member > w/o any problems. > > > Is this expected behavior? Are there any potential problems if i > stick with metadata=0.90(apart from the 28 device and 2Tb disk space > limit)? > Yes, this is expected behaviour (as Mikael explained). As for potential problems, the big one is if you mount a member of a raid1 array (with metadata 0.90, 1.0) directly, and write to it, you'll corrupt the raid1 array. So make sure you only mount it read-only, unless you never want to see the raid1 again. Typical uses of such mounts are for recovery purposes, or for accessing the raid from a bootloader (newer grub can understand more raid arrays, but raid1 with metadata 0.90 is often used with older grub).