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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 http://nbd.sf.net/.
+ 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.