Hi,

It seems Ceph doesn't allow rados pool snapshots on RBD pools which have or had 
RBD snapshots. They only work on RBD pools which never had a RBD snapshot. 

So, basically this works:

rados mkpool test-pool 1024 1024 replicated
rbd -p test-pool create --size=102400 test-image
ceph osd pool mksnap test-pool rados-snap

But this doesn't:

rados mkpool test-pool 1024 1024 replicated
rbd -p test-pool create --size=102400 test-image
rbd -p test-pool snap create test-image@rbd-snap
ceph osd pool mksnap test-pool rados-snap

And we get the following error message:

Error EINVAL: pool test-pool is in unmanaged snaps mode

I've been checking the source code and it seems to be the expecte behavior, but 
I did not manage to find any information regarding "unmanaged snaps mode". Also 
I did not find any information about RBD snapshots and pool snapshots being 
mutually exclusive. And even deleting all the RBD snapshots in a pool doesn't 
enable RADOS snapshots again. 

So, I have a couple of questions:

- Are RBD and RADOS snapshots mutually exclusive?
- What does mean "unmanaged snaps mode" message?
- Is there any way to revert a pool status to allow RADOS pool snapshots after 
all RBD snapshots are removed? 

We are designing a quite interesting  way to perform incremental backups of RBD 
pools managed by OpenStack Cinder. The idea is to do the incremental backup at 
a RADOS level, basically using the mtime property  of the object and comparing 
it against the time we did the last backup / pool snapshot. That way it should 
be really easy to find modified objects transferring only them, making the 
implementation of a DR solution easier.. But the issue explained here would be 
a big problem, as the backup solution would stop working if just one user 
creates a RBD snapshot on the pool (For example using Cinder Backup).

I hope somebody could give us more information about this "unmanaged snaps 
mode" or point us to a way to revert this behavior once all RBD snapshots have 
been removed from a pool.

Thanks!

Saludos cordiales,
Xavier Trilla P.
Silicon Hosting

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resolvemos tus dudas técnicas gratis?

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