From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adam Goryachev Subject: Re: Is it possible to create a raid from/over other raids? Date: Thu, 19 Dec 2013 09:37:00 +1100 Message-ID: <52B2238C.4000605@websitemanagers.com.au> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 19/12/13 08:12, Wilson Jonathan wrote: > I realise if it is possible its not going to be the best solution, but a > temp stop gap... > > What I am thinking of doing is while I save up to by my 4'th new disk > for a new raid 6 setup (4 drive raid 6, currently has 3 disks 1 missing) > is it possible to use 3 existing smaller disks, create a raid0 across > them and then add the resulting /dev/dmX as "a disk" where the currently > missing disk is marked as missing. > > EG. /dev/md7 ... /dev/sdb1 /dev/sdc1 /dev/sdd1 missing > > mdadm create /dev/md8 raid0 /dev/sde1 /dev/sdf1 /dev/sdg1 > > mdadm --add /dev/md7 /dev/md8 Yes, this is possible, MD doesn't care what the block device is.... MD uses block devices, and produces block devices... > If it is possible do I need to make sure the order in the conf file > first lists the /md8 then the /md7 or will mdadm see that a raid > contains a raid as a disk and then waits for it before assembling. This might depend on what distribution you use /etc... IMHO, it should work without a problem, but you should try it to confirm that. IMHO, this isn't such a terrible idea, it adds at least some level of protection, although if you can using a 4th smaller disk with RAID5 would be better still. I'm also assuming performance is not a critical factor in all this... BTW, can anyone comment whether this would work: Using linear, then only the portion of the RAID0 with the failed disk will be failed in the RAID6, so 2/3rds will still be 4 disk RAID6 and 1/3rd will be 3 disk RAID6? Regards, Adam -- Adam Goryachev Website Managers www.websitemanagers.com.au