nbd-client

node-nbd-client

Linux NBD client and library for Node.js. Built to automate block storage systems.

Features

• Fast: node-nbd-client can attach an NBD device in ~10ms and does all I/O in parallel. nbd-client does all I/O serially. Transmission is handled by the kernel so it performs exactly the same.
• Persistent connections: will always reconnect, even if nbd-client -disconnect is used. nbd-client will stop if the server crashes, even with -persist.
• Built for containers:
  • ioctl interface by default. nbd-client defaults to the netlink interface which requires --network=host on Docker.
  • node-nbd-client uses threads and never calls fork(), which keep sockets in the calling PID. nbd-client will fork even with -nofork (it is intended per the man page), causing a kernel deadlock if SIGKILL is sent to a container: main process waits for file descriptors to close, which cannot close because the forked process is opened, but the forked process won't quit until the Docker init process quits, which is blocked by the main process, making Docker show a zoombie process error, requiring a machine restart to unlock resources.

Usage

CLI

$ npm install nbd-client --global
$ node-nbd-client --help
Usage: node-nbd-client [options] <device>

<device>

Full path to the block device the client should use, example: /dev/nbd5.

-H, --host <host>

Server hostname or IP address, defaults to localhost.

-P, --port <port>

Server port, defaults to 10809, the IANA-assigned port number for the NBD protocol.

-u, --unix <path>

UNIX domain socket path, overrides TCP options.

-b, --block-size <size>

Block-size in bytes, defaults to 1024; allowed values are either 512, 1024, 2048 or 4096.

-C, --connections <number>

Number of connections to the server, increasing throughput and reducing latency at the cost of higher resource usage. Requires Linux 4.9+.

-N, --name <name>

Configure the export name, defaults to default.

-p, --persist

Configure if the client should always reconnect if the connection is unexpectedly dropped.

-c, --check

Configure if the client should quit with an exit code of 0 if the NBD device is attached or 1 if the NBD device is not attached.

-h, --help

Display help.

Library

Install using npm install nbd-client

import { NBD } from 'nbd-client'

const device = '/dev/nbd0'

if (await NBD.check(device)) {
    throw new Error(`${device} is already attached`)
}

const client = new NBD({
    device,

    name: 'my-disk', // same as nbd-client --name
    socket: { path: 'nbd-server.sock' }, // same options as net.createConnection()
    persist: true, // same as nbd-client --persist
    connections: 4, // same as nbd-client --connections

    connected() {
        console.log('Client connected')
    },
})

// Stop the client after 5 seconds
setTimeout(() => client.stop(), 5000)

console.log('Connecting to NBD..')

// Start the client
await client.start()

console.log('Client stopped')

Not implemented

• netlink interface
• Old-style negotiation