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Based on kernel version 2.6.27. Page generated on 2008-10-13 09:53 EST.

1	                      Network Block Device (TCP version)
2	                                       
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).
14	   
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.
20	   
21	   For more information, or to download the nbd-client and nbd-server
22	   tools, go to http://nbd.sf.net/.
23	
24	   Howto: To setup nbd, you can simply do the following:
25	
26	   First, serve a device or file from a remote server:
27	
28	   nbd-server <port-number> <device-or-file-to-serve-to-client>
29	
30	   e.g.,
31		root@server1 # nbd-server 1234 /dev/sdb1
32	
33		(serves sdb1 partition on TCP port 1234)
34	
35	   Then, on the local (client) system:
36	
37	   nbd-client <server-name-or-IP> <server-port-number> /dev/nb[0-n]
38	
39	   e.g.,
40		root@client1 # nbd-client server1 1234 /dev/nb0
41	
42		(creates the nb0 device on client1)
43	
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.
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