<section id="rbd-primary-storage">

<title>Snaphotting, backups, cloning and System VMs for RBD Primary Storage</title>

<note>

<para>These new RBD features require at least librbd 0.61.7 (Cuttlefish) and libvirt 0.9.14

on the KVM hypervisors.</para>

</note>

<para>With this release &PRODUCT; will leverage the features of RBD format 2. This allows

snapshotting and backing up those snapshots.</para>

<para>Backups of snapshots to Secondary Storage are full copies of the RBD snapshot,

they are not RBD diffs. This because when restoring a backup of a snapshot it is not mandatory

that this backup is deployed on RBD again, it could also be a NFS Primary Storage.</para>

<para>Another key feature of RBD format 2 is cloning and with this release templates will

be copied to Primary Storage once and using the cloning mechanism new disks will be cloned

from this parent template. This saves space and decreases deployment time for Instances

dramatically.</para>

<para>Before this release a NFS Primary Storage was still required for running the System VMs

from. The reason behind this was a so called 'patch disk' which was generated by the hypervisor

which contained metadata for the System VM. The scripts generating this disk didn't support

RBD and thus System VMs had to be deployed from NFS. With 4.2 instead of the patch disk a

VirtIO serial console is used to pass meta information to System VMs. This enabled the deployment

of System VMs on RBD Primary Storage.</para>

</section>