About snapshots on primary storage

[tdtmusic2]

Hi all. Does any of you use the primary storage for storing snapshots? I mean the snapshot.backup.to.secondary set to false. I tried switching to primary (kvm + ceph pool as primary storage) but after that all snapshots are 0 bytes in size and there's no write activity in ceph. Also, if you have more than one primary storage defined, how would the snapshots be saved? Randomly or by some criteria?