+
+==== On POWER ====
+
+There are two KVM implementations on POWER, the KVM-PR (kvm-pr.ko) one which uses the "PRoblem state" of the ppc CPUs to run the guests and the KVM-HV (kvm-hv.ko) one uses the hardware virtualization support of the POWER CPU. In the later case the guest CPU has to be of the same type as the host CPU. However, there is at least the possibility to run the guest in a backward-compatibility mode of the previous CPU generation by using the compat parameter:
+{{{
+ gnt-cluster modify -H kvm:cpu_type='host,\compat=power8'
+}}}
+
+=== Add a virtio-rng device ===
+
+VirtIO RNG (random number generator) is a paravirtualized device that is exposed as a hardware RNG device to the guest. Virtio RNG just appears as a regular hardware RNG to the guest, which the kernel reads from to fill its entropy pool. Unfortunately Ganeti does not support it natively, therefore the kvm_extra option should be used. Ganeti forces the allocation of the PCI devices to specific slots, which means it is not possible to use the QEMU autoallocation and that an explicit PCI slot has to be provided. There 32 possible slots on the default QEMU machine, so we can use one of the last ones for example 0x1e.
+
+The final command to add a virtio-rng device cluster-wise is therefore:
+{{{
+ gnt-cluster modify -H kvm:kvm_extra="-device virtio-rng-pci\,bus=pci.0\,addr=0x1e\,max-bytes=1024\,period=1000"
+}}}
+
+The max-bytes and period options limit the entropy rate a guest can get to 1kB/s.