[one-users] templates and images explanation needed

[pawel.orzechowski at budikom.net]

After reading the ON docs and explanation from panoramisk I understand
the behaviour of persistent vs non-persistent image. But I do not get
idea behind this. It seems to be opposite to ON simplicity. 

We had a following situation: 

 	* the machine was running with non-persistent image disk, 
 	* I created hot snapshot, then I create next but deferred snapshot
 	* Then I thought I do not need deferred snapshot so I deleted the
image
 	* Now when I wanted to create next snapshot I could not because I got
error "the disk 0 will be saved"
 	* In the VM view of this particular VM at storage tab there was my
original non-persistent image but with ID of the deleted image and
information that it is persisent
 	* Now the only way to clear this situation was to shutdown VM which
caused that it was deleted
 	* the last state of data was in the image created from hot snapshot

Based on this and also our current experience with VMware or XenServer
environments I do not really get this image/template idea in OpenNebula,
so please again can someone clarify: 
1. What is the "business" purpose of a non-persistent image? What are
use cases here? (I suppose one is some goldencopy) 
2. Can the deployment of virtual machine with persistent image from
non-persistent image be simpler? Now having non-persistent image (eg.
from ON marketplace) one has to clone it than change it to persistent,
then create template with this image and then instantiate virtual
machine from this. Now when I want to create another, bunch of virtual
machines with persistent images I have to create bunch of copies of
non-persistent image and create image with each of them and then from
each instantiate VM - this is not simple but it should be. 
3. In the case of this persistent images what is the case for template
here, if I can not use template twice - once I create VM from template
with persistent image I can not used it again because image is
persistent and data is being written to him - the solution here is that
while creating VM from "persistent" template it should automatically
copy image to a new one for use in VM so the next VM could be created. 
4. If I have VM running with non-persistent image there should be a way
to switch VM to persistent image without loosing data. 

Thanks 

Pawel 
-- 

Paweł Orzechowski
pawel.orzechowski at budikom.net
BUDIKOM.NET
 
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