such as filenames, directories, access permissions, and file layout. The MDT data is stored in a local disk filesystem. However, unlike block-based distributed filesystems, such as GPFS and PanFS, where the metadata server controls all of the block allocation, the Lustre metadata server is only involved in pathname and permission checks, and is not involved in any file I/O operations, avoiding I/O scalability bottlenecks on the metadata server. The ability to have multiple MDTs in a single filesystem is a new feature in Lustre 2.4, and allows directory subtrees to reside on the secondary MDTs, while 2.7 and later allow large single directories to be distributed across multiple MDTs as well. One or more object storage server (OSS) nodes that store file data on one or more object storage target (OST) devices. Depending on the server's hardware, an OSS typically serves between two and eight OSTs, with each OST managing a single local disk filesystem. The capacity of a Lustre file system is the sum of the capacities provided by the OSTs. Client(s) that access and use the data. Lustre presents all clients with a unified namespace for all of the files and data in the filesystem, using standard POSIX semantics, and allows concurrent and coherent read and write access to the files in the filesystem. The MDT, OST, and client may be on the same node (usually for testing purposes), but in typical production installations these devices are on separate nodes communicating over a network. Each MDT and OST may be part of only a single filesystem, though it is possible to have multiple MDTs or OSTs on a single node that are part of different filesystems. The Lustre Network (LNet) layer can use several types of network interconnects, including native InfiniBand verbs, Omni-Path, RoCE, and iWARP via OFED, TCP/IP on Ethernet, and other proprietary network technologies such as the Cray Gemini interconnect. In Lustre 2.3 and earlier, Myrinet, Quadrics, Cray SeaStar and RapidArray networks were also supported, but these network drivers were deprecated when these networks were no longer commercially available, and support was removed completely in Lustre 2.8. Lustre will take advantage of remote direct memory access (RDMA) transfers, when available, to improve throughput and reduce CPU usage. The storage used for the MDT and OST backing filesystems is normally provided by hardware RAID devices, though will work with any block devices. Since Lustre 2.4, the MDT