Ceph RBD can technically support multi-writer access through exclusive locking, but it won't be the same as multi-writer.

You can set up a radosgw outside of the proxmox and use objects.

But ceph is fundamentally a distributed object store, shared LUNs with block level multi-writer is fundamentally a tightly coupled solution.

If you have a legacy need that has OCFS or a quorum drive, the underlying tools proxmox is an abstraction can sometimes be used as these types of systems tend to be pets.

But if you were just using multi-writer because it was there, there are alternatives that are typically more robust under the shared nothing model like Ceph uses.

But it is all tradeoffs and horses for courses.

> But ceph is fundamentally a distributed object store, shared LUNs with block level multi-writer is fundamentally a tightly coupled solution.

There is Ceph and then there is CephFS, "a POSIX-compliant file system built on top of Ceph’s distributed object store, RADOS":

* https://docs.ceph.com/en/latest/cephfs/

* https://pve.proxmox.com/wiki/Storage:_CephFS

From what I read about VMFS yes ceph allows you to have a shared block devices (RBD = rados block devices) across a cluster, and proxmox VE HA makes sure only one instance of the VM is active on the cluster to avoid having multiple writers to the same disk image.