Hello Humberto
On 13.10.2011 11:03, Humberto N. Castejon Martinez wrote:
Reading the Opennebula documentation, I believe there are two things I have
to deal with:
1) The image repository, and whether it is shared or not between the
front-end and the workers
I have some persistent Images which are used for "persistent"
VMs. I have the images folder shared with NFS and I use tm_nfs.
When starting a VM with a persistent images, it creates only a
soft link in VM_DIR which points to the image in the images
folder. If you want to have copied the persistent image into the
VM_DIR on the cluster node, you would need tm_ssh. But then on
startup the whole image will be copied to the cluster node into
VM_DIR and on shutdown it will be copied back to the images folder.
2) The<VM_DIR>, that contains deployment files, etc for the VMs running on
a worker. This directory may or not be shared between the front-end and the
workers, but it should always be shared between the workers if we want live
migration, right?
If you use tm_ssh you do not need to share this, if you use
tm_nfs, you need to have it shared. The same with the images
folder. For live migration you need a shared images folder and
VM_DIR.
Some of the questions I have are these (sorry if some of them seem stupid
:-)):
They are not stupid, It took me some time to try out and see
through how this things works, and so I had to change my setup a
few times until OpenNebula an I were happy.
- What are the implications of sharing or not the image repository between
the front-end and the workers (apart from the need to transfer images to the
worker nodes in the latter case)?
See above.
- What are the implications of sharing or not the<VM_DIR> between the
front-end and the workers?
Also above.
- Can I use ZFS or MooseFs and still be able to live migrate VMs?
MooseFS [1] is a fault tolerant, network distributed file system
(eg. over several servers). I do not know if ZFS can do this.
MooseFS is similar like NFS, only that the data are distributed
over several servers (including your local server). I guess live
migration should work.
[1] http://www.moosefs.org/
- Will the<VM_DIR> always hold a (copy of a) VM image for every VM running
on a worker? Must the<VM-DIR> be in the local hard drive of a worker or may
it reside on an external shared storage?
See above, if used with tm_nfs, it is on a external shared
storage (NFS server). When used with tm_ssh, it is on the local
disk and all images (public or persistent) will be copied in full
through ssh.
I guess two factors i should also consider when choosing a solution are the
following, right?
- The speed of transferring VM images
- The speed of cloning VM images
Yes. Access to a persistent image through NFS only transfers the
data needed, cloning always creates a full copy. When you use
tm_ssh, the image will always be copied in full through ssh
(which also gives some CPU overhead on the front end and cluster
node).
I hope this helps and my information are correct, if not, could
somebody from OpenNebula please correct me.
bye
Fabian
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