actual size of the granted lock depends on several factors, including the number of currently granted locks on that object, whether there are conflicting write locks for the requested lock extent, and the number of pending lock requests on that object. The granted lock is never smaller than the originally requested extent. OST extent locks use the Lustre FID of the object as the resource name for the lock. Since the number of extent lock servers scales with the number of OSTs in the filesystem, this also scales the aggregate locking performance of the filesystem, and of a single file if it is striped over multiple OSTs. Networking The communication between the Lustre clients and servers is implemented using Lustre Networking (LNet), which was originally based on the Sandia Portals network programming application programming interface. Disk storage is connected to the Lustre MDS and OSS server nodes using direct attached storage (SAS, FC, iSCSI) or traditional storage area network (SAN) technologies, which is independent of the client-to-server network. LNet can use many commonly used network types, such as InfiniBand and TCP (commonly Ethernet) networks, and allows simultaneous availability across multiple network types with routing between them. Remote Direct Memory Access (RDMA) is used for data and metadata transfer between nodes when provided by the underlying networks, such as InfiniBand, RoCE, iWARP, and Omni-Path, as well as proprietary high-speed networks such as Cray Aries and Gemini, and Atos BXI. High availability and recovery features enable transparent recovery in conjunction with failover servers. Since Lustre 2.10 the LNet Multi-Rail (MR) feature allows link aggregation of two or more network interfaces between a client and server to improve bandwidth. The LNet interface types do not need to be the same network type. In 2.12 Multi-Rail was enhanced to improve fault tolerance if multiple network interfaces are available between peers. LNet provides end-to-end throughput over Gigabit Ethernet networks in excess of 100 MB/s, throughput up to 11 GB/s using InfiniBand enhanced data rate (EDR) links, and throughput over 11 GB/s across 100 Gigabit Ethernet interfaces. High availability Lustre file system high availability features include a robust failover and recovery mechanism, making server failures and reboots transparent. Version interoperability between successive minor versions of the Lustre software enables a server to be upgraded by taking it offline (or failing it over to a standby server), performing the upgrade, and restarting it, while all active jobs