Share reservations are a new concept in the NFS version 4 protocol and are different than byte-range locking. Share reservations provide a method for controlling access to a file. When an OPEN request is sent for a file, the requester can indicate the type of access that should be denied to other requesters attempting to access the same file, which is NONE, READ, WRITE or BOTH.

Share reservations have an advantage over byte-range locking in that they provide a mandatory locking interface; any application that attempts to OPEN a file that is already opened and locked by another application is denied access. However, in these cases, access to files (and application processing) may be slowed if files are not shared.