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- Network Block Device (TCP version)
- What is it: With this compiled in the kernel (or as a module), Linux
- can use a remote server as one of its block devices. So every time
- the client computer wants to read, e.g., /dev/nb0, it sends a
- request over TCP to the server, which will reply with the data read.
- This can be used for stations with low disk space (or even diskless -
- if you boot from floppy) to borrow disk space from another computer.
- Unlike NFS, it is possible to put any filesystem on it, etc. It should
- even be possible to use NBD as a root filesystem (I've never tried),
- but it requires a user-level program to be in the initrd to start.
- It also allows you to run block-device in user land (making server
- and client physically the same computer, communicating using loopback).
- Current state: It currently works. Network block device is stable.
- I originally thought that it was impossible to swap over TCP. It
- turned out not to be true - swapping over TCP now works and seems
- to be deadlock-free, but it requires heavy patches into Linux's
- network layer.
- For more information, or to download the nbd-client and nbd-server
- tools, go to
- Howto: To setup nbd, you can simply do the following:
- First, serve a device or file from a remote server:
- nbd-server <port-number> <device-or-file-to-serve-to-client>
- e.g.,
- root@server1 # nbd-server 1234 /dev/sdb1
- (serves sdb1 partition on TCP port 1234)
- Then, on the local (client) system:
- nbd-client <server-name-or-IP> <server-port-number> /dev/nb[0-n]
- e.g.,
- root@client1 # nbd-client server1 1234 /dev/nb0
- (creates the nb0 device on client1)
- The nbd kernel module need only be installed on the client
- system, as the nbd-server is completely in userspace. In fact,
- the nbd-server has been successfully ported to other operating
- systems, including Windows.