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@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@gmail.com> Sent: March 31, 2021 05:59 PM To: Tony Liu Cc: openstack-discuss@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@hotmail.com<mailto:tonyliu0592@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