NFS 3.0 vs NFS 4.1 Locking mechanism

NFS 3 locking on ESXi does not use the Network Lock Manager (NLM) protocol. Instead, VMware does provide it's own locking protocol. NFS 3 locks are implemented by creating lock files on the NFS server. Lock files are named .lck-file_id.

NFS 4.1 uses share reservations as a locking mechanism.

File locking mechanisms are used to restrict access to data to only one user or process at a time. NFS 3 and NFS 4.1 file locking mechanisms are incompatible with each other.

Because NFS 3 and NFS 4.1 clients do not use the same locking protocol, you cannot use different NFS versions to mount the same datastore on multiple hosts. Accessing the same virtual disks from two incompatible clients might result in incorrect behavior and cause data corruption.