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I have CentOS 7, and I want lvm mirrors on my root logical volume.

I had some panic after I used "lvconvert -m3 cl_excalibur/root" to create two mirrors, and it would not boot. The logical volume does not activate at boot when it is raid1. I booted from a liveUSB, and used "lvconvert -m0" to convert it back to un-mirrored, and all seems well. But I'm back to square one. I expect I must use dracut -f --add<-drivers?> <name of the lvm raid kernel module>, but I don't know the exact arguments I need.

During a failed boot, in the dracut lvm tool, I tried lvchange -ay cl_excalibur/root, but lvm complained that the module "dm-raid" was not in the kernel. So that's what I think I need to install.

I found the file /usr/lib/modules/3.10.0-1062.1.1.el7.x86_64/kernel/drivers/md/dm-raid.ko.xz. However, I don't know which add flag to use, nor how to go from the filename above to the argument dracut requires.

This host is important to our infrastructure, so I have not yet tried anything. I've now built a virtual CentOS 7 server so I can hack around with dracut and grub2, but I'll appreciate any help :)

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  • Did you try no arguments? dracut should automatically detect which modules are needed.
    – Michael Hampton
    Sep 29, 2019 at 6:02
  • "No arguments" dracut -fdid not work, but I used the virtual machine to figure out the solution. See below.
    – Charlweed
    Sep 29, 2019 at 20:13

1 Answer 1

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It looks like the solution is to edit /etc/dracut.conf, insert some strings into the assignments for add_dracutmodules and add_drivers, and enable the "yes" values for mdadmconf and lvmcomf: 

# dracut modules to add to the default
add_dracutmodules+="dm lvm dmraid mdraid"

# additional kernel modules to the default
add_drivers+="dm_mod dm_mirror dm_log dm_region_hash "

# install local /etc/mdadm.conf
mdadmconf="yes"

# install local /etc/lvm/lvm.conf
lvmconf="yes"

The only wacky part is that I needed to include a space after the last kernel driver, and before the closing quote. Otherwise dracut concatenates two driver names into one.

After using lvconvert -m2 on the root logical volume, I waited for the mirroring to complete by checking with lvs -a -o name,copy_percent,devices centos_agamemnon. Then I proceeded with 

dracut -f 
grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg

And rebooted. All seems fine, and I'm less vulnerable to the next, inevitable, hard drive failure.

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