Ganeti is a cluster virtual server management software tool built on top of existing virtualization technologies such as Xen or KVM and other open source software.

Ganeti Repo

Ganeti Docs

On the Ganeti Repo side you find a pretty good tutorial. Here is just a litte summary for RHEL/CentOS 7 and useing KVM.

You will have some strange problems, This should help you out.

You almost tried Restoring redundancy for DRBD-based instances and had no success. Take a look if you have some active LV's from your DRBD and deactivate it.

# lvscan
...
  ACTIVE            '/dev/vg_yourVM/lv_disk' [10.00 GiB] inherit
...
# gnt-cluster command vgchange -an vg_yourVM

Now you should be able to start your VM.

Somehow the DRBD-disks from the VM are visible on the host and you have to remove them. Check if there is a DRBD-disk mounted and unmount it.

grep -i drbd /proc/mounts

After that, take a look at the device mapper itself.

dmsetup ls
dmsetup remove drbd0-0

Remove all DRBD-disks that are listed by dmsetup.