Xena and CEPH RBD backend (show_image_direct_url status )

Tony Liu tonyliu0592 at hotmail.com
Sun Apr 10 02:39:42 UTC 2022

To clarify, what I did was to create a snapshot of VM based on image.
Is it because Nova doesn't get the image location from Glance?

From: Tony Liu <tonyliu0592 at hotmail.com>
Sent: April 9, 2022 07:28 PM
To: Erno Kuvaja; west, andrew
Cc: openstack-discuss at lists.openstack.org
Subject: Re: Xena and CEPH RBD backend (show_image_direct_url status )

Hi Erno,

I have a Xena setup with Ceph.
When create a snapshot of an image, it is a full copy.
When create a volume from an image, it is an incremental copy.
show_multiple_locations is true.
show_image_direct_url doesn't seem having effect, true or false,
the same result.

With Ussuri, both of above 2 creations are incremental copy.

Is there any way we can do incremental snapshot for image?

From: Erno Kuvaja <ekuvaja at redhat.com>
Sent: March 16, 2022 06:33 AM
To: west, andrew
Cc: openstack-discuss at lists.openstack.org
Subject: Re: Xena and CEPH RBD backend (show_image_direct_url status )

On Thu, Feb 24, 2022 at 2:37 PM west, andrew <andrew.west-contractor at cgg.com<mailto:andrew.west-contractor at cgg.com>> wrote:
Hello experts

Currently using openstack Xena and Ceph backend (Pacific 16.2.7)

It seems there is a bug (since Wallaby?) where the efficient use of a CEPH Pacific RBD backend (i.e with copy-on-write-cloning) is not working .
Show_image_direct_url needs to be False to create volumes (or ephemeral volumes for nova)

This can of course be tremendously slow (Nova  , ephemeral root disk) without copy-on-write cloning feature of Ceph.

As Ceph RBD is THE most favourite  backend for block storage in openstack I am wondering how others are coping (or workarounds found ?)
Which combinations of Openstack and Ceph  are known to work well with copy-on-write-cloning?

How is the noted GRAVE Security RISK  of enabling Show_image_direct_url mitigated  ?  (i.e I think , for CEPH RBD, it needs to  be True to get cloning to work efficiently)

See another report of this issue here:
Re: Ceph Pacifif and Openstack Wallaby - ERROR cinder.scheduler.flows.create_volume — CEPH Filesystem Users (spinics.net)<https://www.spinics.net/lists/ceph-users/msg66016.html>

Thanks for any help or pointers,

Andrew West
Openstack consulting
CGG France

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Hi Andrew,

Sorry for the delayed reply. I got distracted and forgot after the first time I noticed this.

So far I see you only mentioning 'show_image_direct_url' setting but AFAIK also the 'show_multiple_locations' is required for these features to work, is that set true and the issue still persists?

- jokke

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