There is one issue with Active/Actvie cinder cluster. Each cinder-volume instance in cluster holds it's own local allocated_capacity_gb. When cinder-volume service starts it counts all volumes created on particular pool and calculates allocated_capacity_gb accordingly. If one instance of cinder-volume create volume - it increase  its local allocated_capacity_gb. If other instance delete volume - it decrease its local allocated_capacity_gb. And each instance of cinder-volume in cluster reports its own local allocated_capacity_gb. It cause incorrect allocated_capacity_gb presented to cinder get-pools --detail. And it is able to see even negative value of allocated_capacity_gb for pool.

There is reported issue about it:

https://bugs.launchpad.net/cinder/+bug/1927186

There is document about different approaches of Active-Active cinder support, but there is nothing about incorrect allocated_capacity_gb report on it:

https://docs.openstack.org/cinder/latest/contributor/high_availability.html

Looks like without fixing allocated_capacity_gb we have to get all valumes and calculate this value by portal (it isnt quite effective and resource consuming by the way).

Are there any plans to complete Active/Active support for cinder ? 

For example as the coordinator is demand for Active/Active support

(“My recommendation is to do this right: configure the cluster option,

remove the backend_host, and configure the coordinator.”, https://lists.openstack.org/pipermail/openstack-discuss/2020-November/018853.html)