From mboxrd@z Thu Jan 1 00:00:00 1970 From: Subject: [BUG] non-metadata arrays cannot use more than 27 component devices Date: Fri, 24 Feb 2017 04:08:16 -0800 Message-ID: <20170224040816.41f2f372.ian_bruce@mail.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids When assembling non-metadata arrays ("mdadm --build"), the in-kernel superblock apparently defaults to the MD-RAID v0.90 type. This imposes a maximum of 27 component block devices, presumably as well as limits on device size. mdadm does not allow you to override this default, by specifying the v1.2 superblock. It is not clear whether mdadm tells the kernel to use the v0.90 superblock, or the kernel assumes this by itself. One or other of them should be fixed; there does not appear to be any reason why the v1.2 superblock should not be the default in this case. details are here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=855871 This problem is easy to reproduce, even with simple hardware. You can use /dev/loop devices as the array components, as explained in the link. -- Ian Bruce