It works in the literal sense, but you should really try it as bare metal. You will notice a huge difference in latency and performance when doing any kind of metadata operations, and this effect is compounded as you get to millions of objects. My cluster has 1.1 billion objects.my moosefs-leader is a VM and it does not seem to causing me any problems. VM host is promox on a intel E5v4 based cpu system with ddr4. My usage of moosefs is mostly vm backups from promox or media files for plex. Current moosefs cluster is 135tb total, 80tb free. 150k fs objects 563k chucks. The chuckservers are all proxmox hosts again intel E5v4 based cpu system with ddr4, 19 disk spread over 3 nodes.