[Openstack-operators] Mixed env for nova (ceph for some compute nodes, local disk for the rest): qcow2 or raw images ?

Massimo Sgaravatto massimo.sgaravatto at gmail.com
Wed Apr 5 14:31:04 UTC 2017

Hi George

Thanks for your feedback

Yes, it makes sense, but most of our users upload their own images.
Educating them to upload the image twice and setting the metadata on these
images won't be easy at all

Thanks, Massimo

2017-04-05 16:23 GMT+02:00 George Mihaiescu <lmihaiescu at gmail.com>:

> Hi Massimo,
> You can upload the images twice, in both qcow2 and raw format, then create
> a host aggregate for your "local-disk" compute nodes and set its metadata
> to match the property you'll set on your qcow2 images.
> When somebody will start a qcow2 version of the image, it will be
> scheduled on your compute nodes with local disk and pull the qcow2 image
> from Glance.
> Does it make sense?
> George
> On Wed, Apr 5, 2017 at 10:05 AM, Massimo Sgaravatto <
> massimo.sgaravatto at gmail.com> wrote:
>> Hi
>> Currently in our Cloud we are using a gluster storage for cinder and
>> glance.
>> For nova we are using a shared file system (implemented using gluster)
>> for part of the compute nodes; the rest of the compute nodes use the local
>> disk.
>> We are now planning the replacement of gluster with ceph. The idea is
>> therefore to use ceph for cinder, glance. Ceph would be used for nova but
>> just for a set of compute nodes  (the other compute nodes would keep using
>> the local disk).
>> In such configuration I see a problem with the choice of the best format
>> type
>> for images.
>> As far as I understand (please correct me if am wrong) the ideal setup
>> would be using raw images for VMs targeted to compute nodes using ceph, and
>> qcow2 images for VMs targeted to compute nodes using the local disk for
>> nova.
>> In fact starting a VM using a qcow2 image on a compute node using ceph
>> for nova works but it is quite inefficient since the qcow2 image must be
>> first downloaded in /var/lib/nova/instances/_base and then converted into
>> raw. This also means that some space is needed on the local disk.
>> And if you start a VM using a raw image on a a compute node using the
>> local disk for nova, the raw image (usually quite big) must be downloaded
>> on the compute node, and this is less efficient wrt a qcow2 image. It is
>> true that the qcow2 is then converted into raw, but I think that most of
>> the time is taken in downloading the image.
>> Did I get it right ?
>> Any advice ?
>> Thanks, Massimo
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