We currently run Citrix XenServer as our virtualization platform. After running for a few years on iSCSI, we switched to NFS (flakey iSCSI hardware and snapshots).
One thing XenServer does is zero downtime NFS snapshots, using a copy-on-write system. When the snapshot is removed, it 'coalesces' the original file and the new cow file.
Are there plans to implement a zero downtime NFS snapshot solution for Proxmox? Or better yet, a GlusterFS one?