From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Klingner Subject: Re: raid1 with rotating offsite disks for backup Date: Mon, 7 Feb 2011 17:32:48 -0800 Message-ID: <47409A64-9CF1-4E12-9DAD-F7079298B1FE@stanford.edu> References: <1ADCC31C-C4BD-4D43-829F-9341D3663185@stanford.edu> <20110208111743.1479308d@notabene.brown> <20110208121923.5908630d@notabene.brown> Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <20110208121923.5908630d@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids >>>> Also, if you want two rotating backups I would create two stacked raid1s. >>>> >>>> mdadm -C /dev/md0 -l1 -n2 -b internal /dev/main-device /dev/first-backup >>>> mdadm -C /dev/md1 -l1 -n2 -b internal /dev/md0 /dev/second-backup >>>> mkfs -j /dev/md1 On Feb 7, 2011, at 5:19 PM, NeilBrown wrote: > I'm surprised that you found the correct advise, and chose not to follow > it ..... Thanks again for your advice. I didn't search the list until after completing my initial setup; my mistake and my lesson learned: research first. > The array you will end up installing on is (slightly) smaller than than the > array you have created. So no: you cannot re-arrange things - you have to > start again. > > > (well, to be honest, it is possible that you could resize whatever is on the > array and then build the secondary array and make it work. But that path is > error-prone and this margin is not large enough to properly describe the > process). Reckless fool that I am, I'm going to try it anyway. Here's my rough plan: 1. Degrade the 3-disk raid1 array by removing two disks, leaving only one, and leaving the array running. 2. Set up the first 2-disk array (md0 in your description) de novo on the two freed disks 3. Move my data from the original raid1 array (with only 1 of three disks present) to the new 2-disk md0 via lvm mirroring 4. Free the third disk by finally taking down the original raid1 array 5. create the second 2-device array (md1) using md0 and the freed third disk. Somehow ensure that the md0 component has primacy for syncing. Jeff