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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