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1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
48 lines
1.9 KiB
Plaintext
48 lines
1.9 KiB
Plaintext
Network Block Device (TCP version)
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What is it: With this compiled in the kernel (or as a module), Linux
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can use a remote server as one of its block devices. So every time
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the client computer wants to read, e.g., /dev/nb0, it sends a
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request over TCP to the server, which will reply with the data read.
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This can be used for stations with low disk space (or even diskless -
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if you boot from floppy) to borrow disk space from another computer.
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Unlike NFS, it is possible to put any filesystem on it, etc. It should
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even be possible to use NBD as a root filesystem (I've never tried),
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but it requires a user-level program to be in the initrd to start.
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It also allows you to run block-device in user land (making server
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and client physically the same computer, communicating using loopback).
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Current state: It currently works. Network block device is stable.
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I originally thought that it was impossible to swap over TCP. It
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turned out not to be true - swapping over TCP now works and seems
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to be deadlock-free, but it requires heavy patches into Linux's
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network layer.
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For more information, or to download the nbd-client and nbd-server
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tools, go to http://nbd.sf.net/.
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Howto: To setup nbd, you can simply do the following:
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First, serve a device or file from a remote server:
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nbd-server <port-number> <device-or-file-to-serve-to-client>
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e.g.,
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root@server1 # nbd-server 1234 /dev/sdb1
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(serves sdb1 partition on TCP port 1234)
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Then, on the local (client) system:
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nbd-client <server-name-or-IP> <server-port-number> /dev/nb[0-n]
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e.g.,
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root@client1 # nbd-client server1 1234 /dev/nb0
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(creates the nb0 device on client1)
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The nbd kernel module need only be installed on the client
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system, as the nbd-server is completely in userspace. In fact,
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the nbd-server has been successfully ported to other operating
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systems, including Windows.
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