On Tue, 20 Nov 2012 12:36:52 +0000 Benjamin ESTRABAUD <be@xxxxxxxxxx> wrote: > 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! I don't really understand what your problem is. mdadm should create any devices it needs - unless it detects udev, in which case it leaves the device creation to udev. So simply don't create any md devices in /dev and let mdadm do whatever is required. Does that approach not suit your needs? If not, why not? NeilBrown
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