From mboxrd@z Thu Jan 1 00:00:00 1970 From: Veljko Subject: Re: Linear device of two arrays Date: Fri, 14 Jul 2017 15:40:40 +0200 Message-ID: <1eefd627-1aba-a795-05f0-d2106d3a62a3@gmail.com> References: <20170705214250.0ea99538@natsu> <595D2ADA.8010907@youngman.org.uk> <5afd5cea-06b8-8524-e4f5-8534f23bd714@hardwarefreak.org> <87van15j9b.fsf@notabene.neil.brown.name> <87o9sn232n.fsf@notabene.neil.brown.name> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87o9sn232n.fsf@notabene.neil.brown.name> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/14/2017 03:57 AM, NeilBrown wrote: > > Presumably you also have an md3 raid10 which you want to attach to the > end of md2? Yes, I just created it. It's resyncing. > md2 is 5761631232 sectors. > 2880815616 kilobytes > 2813296.5 (binary)megabytes. > > When you include that into a "linear" you will lose a few K from the > end. > It might be sensible to cause the "linear" to use whole stripes from > the raid10, where a stripe is 1M (2 512K chunks). > If you did that, you would lose a little over 1M. > So backup the last 3.5 M of the raid10. This is much more than you need. > > ie. > > dd if=/dev/md2 of=SOMEWHERE/SAFE bs=1M skip=2813293 I'm little confused. What I'm backuping is last 3.5M of used space, right? How is that only ~2.7T? df shows 4.8T of used space. Rest of the instructions are clear and I'll try it as soon as md3 is synced. Thanks Neil! > (dd treats 'M' as 1024*1024, MB is 1000*1000) > > If the file this creates is not 3.5M, then something went wrong. Stop > here. > > Just to be safe you might want to backup the first few megabytes. You > won't need this unless something goes wrong > dd if=/dev/md2 of=SOMEWHERE/ELSE bs=1M count=10 > > Now create the linear from /dev/md2 and /dev/md3(?). Be sure to use > "-e 1.0 --data-offset=0". This creates /dev/md4 > > Now restore the first backup > > dd if=SOMEWHERE/SAFE of=/dev/md4 bs=1M seek=2813293 > > Be sure to use the same bs= and seek= as you did the first time. > Be sure it is copying from the back and to the new linear raid. > > You should now be done. Check your xfs filesystem, and maybe even mount > it and use it. > > NeilBrown > >> >> # mdadm --detail /dev/md2 >> /dev/md2: >> Version : 1.2 >> Creation Time : Fri Sep 14 12:40:13 2012 >> Raid Level : raid10 >> Array Size : 5761631232 (5494.72 GiB 5899.91 GB) >> Used Dev Size : 2880815616 (2747.36 GiB 2949.96 GB) >> Raid Devices : 4 >> Total Devices : 4 >> Persistence : Superblock is persistent >> >> Update Time : Mon Jul 10 12:32:51 2017 >> State : clean >> Active Devices : 4 >> Working Devices : 4 >> Failed Devices : 0 >> Spare Devices : 0 >> >> Layout : near=2 >> Chunk Size : 512K >>