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root disk for instance


> I'm referring this link
> https://docs.openstack.org/mitaka/admin-guide/compute-images-instances.html
> to understand about root disk. In this it is saying root disk will come
> from compute node. What is the location of root disk on compute node?

First, use a later release, Mitaka is quite old, Stein is the current release.

If you use a default configuration without any specific backend for  
your instances they will be located on the compute nodes in  
/var/lib/nova/instances/. The respective base images would reside in   
/var/lib/nova/instances/_base, so your compute nodes should have  
sufficient disk space.

> If I want to keep all my vms on shared storage . How to configure it ?

That's up to you, there are several backends supported, so you'll have  
to choose one. Many people including me use Ceph as storage backend  
for Glance, Cinder and Nova.

> Or If I want to keep all my vms on cinder volume. What will be the
> configuration for it on nova and cinder?

I recommend to set up a lab environment where you can learn to set up  
OpenStack, then play around and test different backends if required.  
The general configuration requirements are covered in the docs [1]. If  
you don't want to configure every single service you can follow a  
deployment guide [2], but that will require skills in ansible, juju or  
tripleO. I'd recommend the manual way, that way you learn the basics  
and how the different components interact.

[1] https://docs.openstack.org/stein/install/
[2] https://docs.openstack.org/stein/deploy/


Zitat von Jyoti Dahiwele <jyotishri403 at gmail.com>:

> Thanks for your reply.
> I'm referring this link
> https://docs.openstack.org/mitaka/admin-guide/compute-images-instances.html
> to understand about root disk. In this it is saying root disk will come
> from compute node. What is the location of root disk on compute node?
>
> If I want to keep all my vms on shared storage . How to configure it ?
>
> Or If I want to keep all my vms on cinder volume. What will be the
> configuration for it on nova and cinder?
>
>
> On Thu, 11 Jul 2019, 15:24 Eugen Block, <eblock at nde.ag> wrote:
>
>> Hi,
>>
>> it's always glance that serves the images, it just depends on how you
>> decide to create the instance, ephemeral or persistent disks. You can
>> find more information about storage concepts in [1].
>>
>> If I'm not completely wrong, since Newton release the default in the
>> Horizon settings is to create an instance from volume, so it would be
>> a persistent disk managed by cinder (the volume persists after the
>> instance has been deleted, this is also configurable). The image is
>> downloaded from glance into a volume on your volume server.
>>
>> If you change the Horizon behavior or if you launch an instance from
>> the cli you'd get an ephemeral disk by nova, depending on your storage
>> backend this would be a local copy of the image on the compute node(s)
>> or something related in your storage backend, e.g. an rbd object in
>> ceph.
>>
>> Does this clear it up a bit?
>>
>> Regards,
>> Eugen
>>
>> [1]
>>
>> https://docs.openstack.org/arch-design/design-storage/design-storage-concepts.html
>>
>>
>> Zitat von Jyoti Dahiwele <jyotishri403 at gmail.com>:
>>
>> > Dear Team,
>> >
>> > Please clear me my following doubts.
>> > When I use image from source option  and mini flavor to create an
>> instace,
>> > from which storage pool instance will get root disk ? From cinder or
>> glance?
>>
>>
>>
>>
>>