Ceph RBD speed and snapshot usage improvements for CloudStack 4.4

[Wido den Hollander <wi...@widodh.nl>]

Hi,

I just pushed to commits to master and cherry picked them to the 4.4 
branch to resolve a long outstanding issue with the time it takes to 
deploy templates and back up snapshots of RBD.

The two commits [0][1] also address the space used by RBD snapshots on 
Secondary Storage.

Before librbd (used by Qemu) 0.67.5 (Ceph Dumpling) qemu-img couldn't 
create RBD format images which is required for deploying a template to 
RBD. Format 2 is used to perform layering and snapshotting on RBD images.

The same version of librbd also allows to directly copy a snapshot from 
RBD to QCOW2 or RAW output. Since qemu-img now does the work the 
destination image is sparse instead of a full write of the RBD image's size.

Both patches will make sure that initial deployment of a template on RBD 
is a lot faster and that backing up a RBD snapshot to Secondary Storage 
will consume less time, storage and network bandwidth.

I have to note however, you require at least librbd 0.67.5 on your 
systems in order for these patches work.

I think some people will be very happy with this.

Wido

[0]: 
https://git-wip-us.apache.org/repos/asf?p=cloudstack.git;a=commit;h=95f6f6531260f0e0946eec3212d06b0d71befc9e
[1]: 
https://git-wip-us.apache.org/repos/asf?p=cloudstack.git;a=commit;h=8764692b271d8ac683e616a732845524f77329a2