From mboxrd@z Thu Jan 1 00:00:00 1970 From: hansbkk@gmail.com Subject: Re: [linux-lvm] Q: LVM over RAID, or plain disks? A:"Yes" = best of both worlds? Date: Tue, 30 Nov 2010 14:34:05 +0700 Message-ID: References: <4CF3F7A0.2080108@rjl.com> <4CF4A472.20107@rjl.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4CF4A472.20107@rjl.com> Sender: linux-raid-owner@vger.kernel.org To: Nataraj Cc: linux-raid@vger.kernel.org, linux-lvm@redhat.com List-Id: linux-raid.ids On Tue, Nov 30, 2010 at 2:14 PM, Nataraj wrot= e: >> TopRAID1's LVM is likely to be running over a RAID6 set , so I'm not >> depending on the TopRAID mirroring for reliability, just using it fo= r >> the above volume cloning. > > Your raid 1 backups won't mirror any snapshots of your LV's unless yo= u > specifically setup mirroring of the snapshots after they exist. Ah, getting clearer to me, I was thinking I'd be mirroring the LV itself, but you're right, taking a snapshot and mirroring that is a much better idea. So here's a summary of steps, please confirm: - create a snapshot of a given volume - create a new RAID1 mdN between that and a physical partition (blank= ?) - let that get sync'd up - break the RAID (fail the partition?), remove the drive - delete the snapshot The below is less clear to me, especially if the above is correct: >> If so, would it be possible/better for the host In normal operations >> to mount the underlying LV directly rather than the degraded top-lev= el >> RAID1? > > No, you want to have mdadm assemble the raid volume, even if in degra= ded > mode with only one drive and then access the LV on top of the md devi= ce. > =A0Even if you were able to mount the LV and bypass raid, that would = be > pointless because you would not update the bitmap and superblock and = the > integrety of the raid set would be lost. During normal operations - when I'm not in the process of taking a RAID-backup of my LV snapshot - it seems to me that the "Top-RAID" mdN doesn't even exist right? It's set up to mirror between a snapshot and a regular partition, both of which don't even exist during these normal operations. Therefore during normal operations the host *is* mounting the LV directly, not via the "Top-RAID"mdN. I wasn't talking about accessing the "Bottom-RAID" which creates the underlying PV - this is transparent to LVM anyway, right? Thanks again for your help (or in advance to anyone else who would like to chime in) -- 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