Use cases for persistent & non-persisent


#1

Hi there,

Sorry, it’s another persistent vs non-persistent question I’m afraid but we’re new to OpenNebula and cloud concepts as a whole.

I’ve taken a look at the various discussions on the community and my general understanding is that a persistent image will remain available for use if a VM is deleted and that a non-persistent image is removed alongside the VM.

What I’m not clear about is when you would opt to use a persistent image and when you’d opt to use a non-persistent image. Could anyone provide any feedback on use cases whereby a persistent image would be preferred over non-persistent? It feels like a stupid question but I feel some context or example services/use cases would help me better understand why you’d use a persistent image & how it may benefit us.

In our case, our VMs will never be terminated/deleted unless the service & data itself is no longer needed and as a result, our initial VMs are running on non-persistent images so that we can use the images we’ve created to spin up new servers easily.

Thank you for your time


(Sergio Semedi Barranco) #2

Hi ryn,

Im going to put a brief example:

NO_PERSISTENCY:

OpenNebula copies the base image (original) to spawn vms, when you are about to terminate the vm you are going to lose all changes performed by the vm itself due to the new copied disk is going to be removed in terminate action.

PERSISTENCY:

Same as above but when you performs any change in the persistent disk, you are writing in the base image as well. That means that all the changes are saved so if you terminate the machine instead of delete the disk you are going to “modify” the base image making the changes permanent.

SMALL USE CASE:

You have a template with ubuntu, you want to modify the base image so you instantiate it as persistent, you start to install some software in Disk (whatever), you think that your new ubuntu is ready so you terminate the machine and use the new image (with all the software) to instantiate new vms.

Regards.


#3

Hi Semedi,

Thank you for the detailed reply and example use case, that’s perfect!

All the best