[openstack-dev] [nova][cinder] Should we allow this kind of action?

hao wang sxmatch1986 at gmail.com
Mon Jul 27 02:49:39 UTC 2015

I wonder why user need to use this kind of image(vm snapshot) to create
volume, and then use this volume to create a vm again. It's meaningless I
think. On the other hand, if an image size is zero, cinder shouldn't allow
to create this volume from image.

2015-07-27 9:39 GMT+08:00 Zhenyu Zheng <zhengzhenyulixi at gmail.com>:

> Hi all,
> Recently, I've been asked to perform this kind of action using OpenStack:
> 1. Launch an volume-backended instance.
> 2. Take a snapshot of this instance using nova image-create, an image will
> be added in glance, the size is zero, and the BDM will be saved in it's
> metadata.
> 3. Create an volume using this image (with Cinder), This volume will be
> marked with bootable.
> 4. Launch an new volume-backended instance using this newly built volume.
> There will be errors performing this action:
> 1. Cinder will create an volume with zero size and the BDM saved in
> metadata is transformed from dict to string and it is not able to be used
> in nova for instance creation.
> 2. The BDM is provided by user with REST API, and it will be conflict with
> the BDM saved in metadata.
> Now, my question is:
> Should we allow this kind of action in Nova? Or should we only use the
> image directly for instance creation.
> If this kind of action is not allowed, should we add checks in Cinder to
> forbid volume creation with an zero-sized image?
> Thanks,
> BR,
> Zhenyu
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Best Wishes For You!
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