Techniques are provided for synchronous replication for synchronous mirror copy guarantee. A file system dependent technique for synchronous mirror copy guarantee is provided by overriding default behavior of a persistent fence so that the persistent fence is activated to block operations targeting a storage object having a synchronous replication relationship based upon the synchronous replication relationship being out of sync. The default behavior of the persistent fence is overridden to allow operations to be executed upon the storage object based upon the synchronous replication relationship being in sync. A file system independent technique for synchronous mirror copy guarantee is provided by intercepting operations before the operations are received by a file system. The operations are selectively forwarded to the file system or not based upon a state of a synchronous replication relationship.