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On Linux, network block device (NBD) is a network protocol that can be used to forward a block device (typically a hard disk or partition) from one machine to a second machine. As an example, a local machine can access a hard disk drive that is attached to another computer.

• Overview

• Alternative protocols

• References

• External links

The protocol was originally developed for Linux 2.1.55 and released in 1997.cite-ref-1[1] In 2011 the protocol was revised, formally documented, and is now developed as a collaborative open standard. There are several interoperable clients and servers.

There are Linux-compatible NBD implementations for FreeBSD and other operating systems. The term 'network block device' is sometimes also used generically.

Technically, a network block device is realized by three components: the server part, the client part, and the network between them. On the client machine, which uses the exported device node, a kernel driver implements a virtual device. Whenever a program tries to access the device, the kernel driver forwards the request (if the client part is not fully implemented in the kernel it can be done with help of a userspace program) to the server machine, on which the data reside physically. On the server machine, requests from the client are handled by a userspace program.

Network block device servers are typically implemented as a userspace program running on a general-purpose computer. All of the function specific to network block device servers can reside in a userspace process because the process communicates with the client via conventional sockets and accesses the storage via a conventional file system interface.

The network block device client module is available on Unix-like operating systems, including Linux.

• iSCSI: The "target-utils" iscsi package on many Linux distributions.

• NVMe-oF: an equivalent mechanism, exposing block devices as NVMe namespaces over TCP, Fibre Channel, RDMA, &c., native to most operating systems

• Loop device: a similar mechanism, but uses a local file instead of a remote one

• DRBD: Distributed Replicated Block Device is a distributed storage system for the Linux platform

• ATA over Ethernet: send ATA commands over Ethernet

• USB/IP: A protocol that provides network access to USB devices via IP.cite-ref-2[2]cite-ref-3[3]

cite-note-11. ↑ "The Network Block Device | Linux Journal".

cite-note-22. ↑ "Documentation/usb/usbip_protocol.txt". kernel.org. 2016-03-21. Retrieved 2017-04-09.

cite-note-33. ↑ "USB over IP tunnel". OpenWrt. 2016-06-17. Retrieved 2017-04-09.

• Network Block Device on GitHub

• nbdkit is a plugin-based NBD server and libnbd is a high-performance C client

• qemu-nbd A nbd tool from qemu project

• BNBD is an alternative NBD server implementation

• xNBD was another NBD server program for Linux

• The Network Block Device, the Linux Journal