LVM2, udev, and multipath [SOLVED]

chardros · Last edited by chardros on Fri Apr 22, 2005 9:29 pm; edited 1 time in total

I've been plugging away at this for about two days... any help would be immensly appreciated. I've got two servers to configure, and haven't gotten the first one to work ideally yet.

I decided to go with LVM2 and am using udev. Everything worked great when building from the live cd. I set up my lvm volumes and groups, and upon doing a vgchange -ay, the groups and voilumes were populated properly in /dev.

I set up one volume group (vg0) and several volumes within it (usr, home, var, etc). After configuring my kernel and booting however, I ran into the issue of volumes appearing as dm-0, dm-1, etc in /dev. I did some research on the forums and found the multipath-tools ebuild. I installed that, vommented the proper lines out in rules and am now using the rule (from 40-multipath.rules):

chardros · Posted: Fri Apr 22, 2005 9:28 pm Post subject: Solved, I think.

OK, I think I solved this...

First, I modified /etc/init.d/checkfs and put --mknodes after vgscan in the LVM2 section. That fixed it. But I wasn't happy cause it felt like a hack.

So, I re-compiled the kernel without --lvm2 in the initrd (as I expected, this is only needed if you're booting to an lvm volume, which I'm not). After test-booting to make sure everything worked (it did), I removed --mknodes from checkfs, restoring checkfs to it's original state. I test-booted again, and again, everything worked fine.

My best guess is, that during boot, with lvm2 in initrd, the lvm2 stuff starts up, populates dev. Then when udev starts, it clobbers what lvm2 had placed there? Does this sound feasible? Doing the --mknodes in checkfs restored it, but it's not needed when you omit lvm2 from initrd... it seems that the first time vgchange -a y is run (which is also ran from checkfs) the device nodes are auto-poulated. When the lvm2 stuff was in initrd, this wasn't happening in checkfs because it wasn't the first time it had ran.

I have NO IDEA if all that speculation is valid... but I'll go with it

.

I had also read this (Gentoo Wiki): http://gentoo-wiki.com/HOWTO_Install_Gentoo_on_an_LVM2_root_partition

In there, he mentions adding --mknodes to checkroot. So I guess if you ARE booting to an lvm2 device, and need the lvm-enabled initrd, the --mknodes alteration is required. But in this case, I don't need all that. root and boot partitions are outside lvm.