Ceph » rbd

Right now the rbd mirror snapshot scheduler (rbd_support mgr module) calls `mirror_image_create_snapshot` synchronously in one thread loop for all mirroring images that require a snapshot. Taking that creating a snapshot is rather long operation (in my test environment it takes more than 1 second) it means that the scheduler has rather low limit of snapshot creation rate.

E.g. if one creates a mirroring pool with 100 images in snapshot mirror mode, and configure global 1 minute interval snapshot schedule, it is most likely the snapshot schedule will be lagging.

It can be improved, e.g. by implementing async version of `mirror_image_create_snapshot` and modifying the scheduler to create snapshots for many images in parallel.