Network block device
On some operating systems, a network block device is a device node whose content is provided by a remote machine. Typically, network block devices are used to access a storage device that does not physically reside in the local machine but on a remote one. As an example, a local machine can access a hard disk drive that is attached to another computer.
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, on which is the device node, a kernel driver controls the 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 resides 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 some Unix-like operating systems, including Linux and Bitrig. Since the server is a userspace program, it can potentially run on every Unix-like platform; for example, NBD's server part has been ported to Solaris.
- iSCSI: The "target-utils" iscsi package on many GNU/Linux distributions. The tgtd can configure the backing storage of a LUN to be any block device (disk, partition, etc.). This has widest adoption amongst IP-based block device presentation protocols.
- 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.
- Patrick Wildt (2015-04-23). "NBD: Implement Network Block Device support". Bitrig.
- Miroslav Kripac (2005-01-21). "Implementing Oracle Real Application Clusters Using Network Block Device Technology". Masaryk University. Retrieved 2016-11-22.
- Mark Peters (2010-01-18). "iSCSI Adoption Continues its Upward Path". Archived from the original on 2016-03-03. Retrieved 2016-11-22.
- "Documentation/usb/usbip_protocol.txt". kernel.org. 2016-03-21. Retrieved 2017-04-09.
- "USB over IP tunnel". OpenWrt. 2016-06-17. Retrieved 2017-04-09.
- Network Block Device on SourceForge.net
- xNBD is another NBD server program for Linux
- BNBD is an alternative NBD server implementation
- nbdkit is a plugin-based NBD server and libnbd is a high-performance C client
- NBD client for FreeBSD on GitHub using GEOM
- nbd-verify aims to be a test kit to verify the protocol implementation as well as a data handling tester of NBD servers
- The Network Block Device, the Linux Journal
- Global Network Block Device (GNBD)
- qemu-nbd A nbd tool from qemu project