mdadm and /dev/md119 /dev/md120 etc

galahad7 · n00b Joined: 18 Mar 2003 Posts: 50

Hi everyone,

I expect this has been asked before, but I haven't been able to find an answer on google or in the forums.

I've been using Gentoo for many years, and know how to set up a kernel and software RAID. However, systems I've setup using the latest live CDs in the last year or so, show mdadm RAIDed drives as /dev/md119, /dev/md120, /dev/md121 etc. Previously, the numbers I set when I created the mdadm nodes, were what the livecd and the kernel used, e.g. /dev/md1, /dev/md2 etc.

Could someone please enlighten me on why the liveCD and new kernels are doing this.

So after setting up with the live cd, one has to try and get the new system booting which is quite a challenge now. For instance, how does one know what grub is seeing (/dev/md? for the root= line), and also what the new kernel will see. I've managed to get these systems going, however I'm not comfortable not knowing what is going on under the covers, and how to fix it if a system breaks in the future.

The software RAID howto could do with an update as well, it doesn't talk about the new /dev/md119, /dev/md120.. etc numbering that I'm seeing. http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml

What would be most helpful is a way to know how GRUB is going to interpret my /dev/mdxxx arrays, and then, how the new kernel is going to interpret the arrays. Ideally, one would somehow uniquely define a partition and use that ID in GRUB and in /etc/fstab.

Thanks for your help
This one has me scratching my head.

Cheers

[n00b@localhost] · Posted: Tue Jun 07, 2011 11:58 am Post subject:

When newer versions of mdadm assemble their arrays they create a node /dev/mdX with X starting at 127 and decreasing for each array found. Each array in newer versions of mdadm also has a name and a symlink is created in /dev/md/ with the name of the array pointing to the actual device. This is the device that grub sees although if your root partition is raid then you will need to assemble it in an initramfs prior to booting. A good guide to this can be found at https://raid.wiki.kernel.org/index.php/RAID_Boot.

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