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.
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.