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4 can use a remote server as one of its block devices. So every time 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 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. 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 - 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. 8 to borrow disk space from another computer.
9 Unlike NFS, it is possible to put any filesystem on it, etc. It should 9 Unlike NFS, it is possible to put any filesystem on it, etc.
10 even be possible to use NBD as a root filesystem (I've never tried), 10
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 11 For more information, or to download the nbd-client and nbd-server
22 tools, go to http://nbd.sf.net/. 12 tools, go to http://nbd.sf.net/.
23 13
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 14 The nbd kernel module need only be installed on the client
45 system, as the nbd-server is completely in userspace. In fact, 15 system, as the nbd-server is completely in userspace. In fact,
46 the nbd-server has been successfully ported to other operating 16 the nbd-server has been successfully ported to other operating