[one-users] Persistent VM image

Alberto Zuin - Liste liste at albertozuin.eu
Mon Sep 5 23:26:04 PDT 2011

Il 06/09/11 07:59, GiBu GeorGe ha scritto:
> Hai...
> My primary language is not english so i am having difficluty in 
> understanding Persistent image concept..
> What i am trying to do is port my existing servers to opennebula.. But 
> i want those vm to act as virtual machine normally would... Means if 
> any changes made to it wont disappear if the server 
> restart(physical/logical).. Does making it persisatant help with that 
> option... Or i am getting it all wrong here..
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When you restart a VM (with restart command) you don't loose anything. 
The same using for example onevm xxx stop.
At the moment there isn't an OpenNebula command to phisically restart a 
VM (like unplug/plug the cable in a physical server) and you have to do 
this in hypervisor (for example in xen with xm destroy xxx/xm create 
xxx): with this operation you don't loose anything.

When you shutdown a VM in OpenNebula you delete disks that are not 
persistent (and then it's correct: persistent images are disk that 
survive when you shutdown a VM in OpenNebula), but this operation is 
like a deletion of a VM, not a simple restart!

The phylosophy on a cloud is a little different than a simple 
virtualization system like VMWare: is to have non persistent "golden" 
disk images with only S.O. and minimal configuration that can be cloned 
to reach the maximum speed when you create a new VM; think this disk 
like a read only disk. Then, in case, there is a second persistent disk 
with persistent data.
For example you can create a VM with a distro like FreeNAS in the non 
persistent disk that export via NFS a persistent volume with you web 
server pages.
Then ther is a second VM with only a webserver configured that read the 
web pages from FreeNAS. When you you reach the maximum load on this VM, 
you can create a second webserver in a couple of seconds to scale your 

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