view Documentation/nbd.txt @ 524:7f8b544237bf

netfront: Allow netfront in domain 0.

This is useful if your physical network device is in a utility domain.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 831230e53067
line source
1 Network Block Device (TCP version)
3 What is it: With this compiled in the kernel (or as a module), Linux
4 can use a remote server as one of its block devices. So every time
5 the client computer wants to read, e.g., /dev/nb0, it sends a
6 request over TCP to the server, which will reply with the data read.
7 This can be used for stations with low disk space (or even diskless -
8 if you boot from floppy) to borrow disk space from another computer.
9 Unlike NFS, it is possible to put any filesystem on it, etc. It should
10 even be possible to use NBD as a root filesystem (I've never tried),
11 but it requires a user-level program to be in the initrd to start.
12 It also allows you to run block-device in user land (making server
13 and client physically the same computer, communicating using loopback).
15 Current state: It currently works. Network block device is stable.
16 I originally thought that it was impossible to swap over TCP. It
17 turned out not to be true - swapping over TCP now works and seems
18 to be deadlock-free, but it requires heavy patches into Linux's
19 network layer.
21 For more information, or to download the nbd-client and nbd-server
22 tools, go to http://nbd.sf.net/.
24 Howto: To setup nbd, you can simply do the following:
26 First, serve a device or file from a remote server:
28 nbd-server <port-number> <device-or-file-to-serve-to-client>
30 e.g.,
31 root@server1 # nbd-server 1234 /dev/sdb1
33 (serves sdb1 partition on TCP port 1234)
35 Then, on the local (client) system:
37 nbd-client <server-name-or-IP> <server-port-number> /dev/nb[0-n]
39 e.g.,
40 root@client1 # nbd-client server1 1234 /dev/nb0
42 (creates the nb0 device on client1)
44 The nbd kernel module need only be installed on the client
45 system, as the nbd-server is completely in userspace. In fact,
46 the nbd-server has been successfully ported to other operating
47 systems, including Windows.