free so they could be used later on next CP cycles and the system will not run out of space with the always-write-new-data-to-new-place policy of WAFL. Only NVLOGs in HA storage systems is replicated synchronously between two controllers for HA storage system failover capability, which helps to reduce overall system memory protection overheads. In a storage system with two controllers in HA configuration or MetroCluster with one controller on each site, each of the two controllers divides its own non-volatile memory into two pieces: local and its partner. In MetroCluster configuration with four nodes, each non-volatile memory divided into next pieces: local, local partner's and remote partner's. Starting with the All-Flash FAS A800 system, NetApp replaced the NVRAM PCI module with NVDIMMs connected to the memory bus, increasing the performance. See also Comparison of file systems List of file systems NetApp NetApp FAS ONTAP Operation System, used in NetApp storage systems Notes External links File System Design for an NFS File Server Appliance (PDF) - Method for maintaining consistent states of a file system and for creating user-accessible read-only copies of a file system - October 6, 1998 WAFL