From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin ESTRABAUD Subject: mdadm: use static major/minor numbers. Date: Tue, 20 Nov 2012 12:36:52 +0000 Message-ID: <50AB7964.60002@mpstor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi! I recently updated mdadm-2.6.9 to mdadm-3.2.6 on a system (own busybox based distro) that had its kernel version updated from 2.6.35 to 3.4. Everything works well apart from a feature I used that I seem to be unable to reactivate: In the past, to ensure knowing the number of possible RAID devices that could be created on the system, I used static major:minor mappings by building the /dev/md/dXX and /dev/md/dXXpXX entries (with major 254, and three minors for each device for 3 partitions), allowing me to be certain that 64 RAID devices could be created at all times. When creating an array, the /dev/md/dXX and dXXpXX devices "nodes" would be used (not recreated) and the major/minor number these devices point to would be used for the actual MD block device. This was a very handy feature. With the latest mdadm, I simply cannot do that, as creating a /dev/md/dXX will in fact remove that device file and symlink it to /dev/md_dXX. I then created /dev/md_dXX devices prior to creating an array, and got the following error message: "mdadm: /dev/md_d3 exists but looks wrong, please fix". Looking through the source I can see that mdadm basically verifies if the file's major/minor matches the one that it had planned for the device, which in this case doesn't. Is there any way to work around that? Or in fact, I don't actually *need* to use static major/minor numbers, but I need to know in advance how many RAIDs I'll be able to create provided I'll always use 2 partitions for them and can provide the -amdp2 argument to mdadm to make sure that only 2 partitions devices nodes are created. Is there a way to know the maximum number of RAIDs that can be created, provided that nothing else uses major 9 and 254? Thank you very much in advance for your help! Regards, Ben.