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BTW,

If the source image is based on compression or thin provision type (like
VDI, QCOW2, VMDK, etc.)
It will take a long time to create no matter boot on image or volume.
Nova will convert the image based on these type first during creation.
Because Ceph RBD doesn't support.
Make sure all the images you upload is based on RBD format (or RAW format
in other word), unless the virtual size of image is small.

.

Tony Liu <tonyliu0592 at hotmail.com> 於 2021年4月1日 週四 上午10:18寫道：

> Thank you Eddie! It makes sense. Creating a snapshot is much faster
> than copying image to a volume.
>
> Tony
> ________________________________________
> From: Eddie Yen <missile0407 at gmail.com>
> Sent: March 31, 2021 05:59 PM
> To: Tony Liu
> Cc: openstack-discuss at lists.openstack.org
> Subject: Re: launch VM on volume vs. image
>
> Hi Tony,
>
> In Ceph layer, IME, launching VM on image is creating a snapshot from
> source image in Nova ephemeral pool.
> If you check the RBD image created in Nova ephemeral pool, all images have
> their own parents from glance images.
>
> For launching VM on volume, it will "copy" the image to volume pool first,
> resize to specified disk size, then connect and boot.
> Because it's not create a snapshot from image, so it will take much longer.
>
> Eddie.
>
> Tony Liu <tonyliu0592 at hotmail.com<mailto:tonyliu0592 at hotmail.com>> 於
> 2021年4月1日 週四 上午8:09寫道：
> Hi,
>
> With Ceph as the backend storage, launching a VM on volume takes much
> longer than launching on image. Why is that?
> Could anyone elaborate the high level workflow for those two cases?
>
>
> Thanks!
> Tony
>
>
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