From mboxrd@z Thu Jan 1 00:00:00 1970 From: Berkey B Walker Subject: Re: Growing a single disk into a 2 disk raid0 Date: Fri, 28 Jan 2011 12:53:58 -0500 Message-ID: <4D4302B6.2090208@panix.com> References: <4D42FA3E.6000206@cfl.rr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4D42FA3E.6000206@cfl.rr.com> Sender: linux-raid-owner@vger.kernel.org To: Phillip Susi Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Phillip Susi wrote: > I had someone wanting to take an existing disk full of data and expand > it by adding a second disk. This seemed reasonable, and I thought of > several ways you could do this, but none of them pan out: > > 1) Create a single disk raid0 using the existing disk, then reshape it > adding the second disk. mdadm fails to add the second disk as a spare > so that you can reshape, with the kernel complaining that personality > does not support diskops. > > 2) Create a single disk raid1 using the existing disk, then reshape it > adding the second disk. Apparently you can not reshape from raid1 to raid0. > > 3) Create a raid10 using the existing disk, setting the number of near > copies to only 1 so as to preserve the existing data, then reshape > adding the second disk. I ran into two problems here: > > a) mdadm refuses to create a single disk raid10, saying that at least > two devices are needed for raid level 4 or 5. I am surprised that you > can not create a single disk raid10 even with --force, and the message > mentions the wrong level. I would think that a single disk raid10 with > 2 far copies would be fairly useful. > > b) I tried 2 disks with one missing and mdadm refuses to create a raid10 > with only a single near copy. The kernel complains that layout 0x101 is > unsupported. > > Is there any way to accomplish this? > > Because 1) I'm old, and 2) I don't trust documentation, I do it the slow, easy way. I use the blank disk and make a RAID missing a disk. I then copy the data to the RAIDed disk. If everything is OK, zero out the old data disk and add it to the raid (filling the "missing"). I do it this way any time I want to make raid of a disk full of data, to any level of raid. b-