nbdkit-S3-plugin(1)

📦
version 1.48.0 · 11 versions
, in ubuntu stonking

💅 nbdkit-S3-plugin(1) — the NBDKIT manual, bestie edition 🦋

okay so we're in the NBDKIT manual section, and today's main character is nbdkit-S3-plugin. bestie, this page is a whole vibe and also extremely useful, so let's go ✨

✨ NAME ✨

nbdkit-S3-plugin — expose data in Amazon S3 or Ceph buckets as a block device 🔥

like literally. your bucket becomes a disk. iykyk.

🌸 SYNOPSIS 🌸

 nbdkit S3 [access-key=...] [secret-key=...] [session-token=...]
           [endpoint-url=...]
           [size=NN object-size=NN]
           bucket=BUCKET key=STRING

that's the whole thing. that's the group chat invite 🫶

👑 DESCRIPTION 👑

nbdkit-S3-plugin is a plugin for nbdkit(1) which lets you open objects stored in Amazon S3 or Ceph as disk images. literally just. disk images. from objects. iconic 💅

This plugin uses the Python Amazon Web Services SDK called Boto3. (yes it's Python, more on why that matters later 👀)

🎀 EXAMPLES 🎀

first one, saving the spot:

 nbdkit S3 endpoint-url=https://ceph.example.com \
           bucket=MY-BUCKET key=disk.img

this one Provides a read only block device holding the data contained in the disk.img object. read only!! don't come for me, that's the spec 💖

second one, the glow-up:

 nbdkit S3 endpoint-url=https://ceph.example.com \
           size=50G object-size=128k \
           bucket=MY-BUCKET key=disk

Provi— ok it provides a read-write block device with size 50G, whose contents are stored multiple in objects of size 128k, prefixed with disk/. yes that's the original wording, it's a little scrambled and we love it anyway 🫶 note: read-write, and it's chunked, and the objects live under a disk/ prefix.

💅 PARAMETERS 💅

okay here's the menu, all of it, no skips:

  • access-key=ACCESS_KEY
  • access-key=+FILENAME
  • access-key=-
  • access-key=-FD
  • secret-key=SECRET_KEY
  • secret-key=+FILENAME
  • secret-key=-
  • secret-key=-FD
  • session-token=SESSION_TOKEN
  • session-token=+FILENAME
  • session-token=-
  • session-token=-FD

— Pass AWS credentials. See CREDENTIALS down below, it's a whole section, we get into it 🔐

  • endpoint-url=ENDPOINT — If accessing Ceph or another compatible S3 service, provide the endpoint URL through this parameter. plain S3? skip it. ceph girlies? this is your moment ✨
  • bucket=BUCKET — The bucket containing the object(s). This parameter is required. like. required required. no bucket, no disk, no vibes 💀
  • key=STRING — The object name (if size is not specified) or object prefix (if size is specified) to use within the bucket. This parameter is required. so it flips meaning depending on size — lowkey important, don't miss it 🎯
  • size=SIZE
  • object-size=SIZE

— These two parameters must always be specified together. always. both or neither, no solo acts 🎀 If set, data will be split into blocks of object-size and stored as separate objects. The block device will report a total size of size and be writeable and trim-able.

Object names will have the form key/%16x, where %16x is the 16-digit hexadecimal block number. If there are existing objects under such name that do not have the expected size, the plugin will crash.

bestie ❗ that last line is real. wrong-sized pre-existing objects = crash. do a vibe check on your bucket before you point this at it 😭

🔥 PERFORMANCE CONSIDERATIONS 🔥

It is highly recommended that clients do their utmost to issue requests that exactly match the object size: Smaller write requests will incur a performance penalty due to the need for read-modify-write cycles (thus also incurring latency from two network round-trips). Larger read and write requests will incur a performance penalty because of sequential execution.

translation: match the object size exactly or you're paying the tax, either way. small = read-modify-write pain plus two round-trips. big = sequential execution pain. the middle path is the slay path 💅

The nbdkit-blocksize-filter(1) can be used to alleviate the impact of requests larger than the object size, but does not help if the client issues requests smaller than the block size. so it fixes the big-request problem only. small requests? it can't save you 🫠

The nbdkit-stats-filter(1) can be used to investigate what block sizes and alignments are used by the client. detective mode 🔍 use it to find out what your client is actually doing.

When connecting through the Linux kernel's NBD module, consider setting /sys/block/nbd<X>/queue/max_sectors_kb to match the object size. yes that's a real path, yes you should go poke it 🧚

🔐 CREDENTIALS 🔐

You can pass AWS credentials in several ways. we love options. we love ✨choices✨

In plaintext on the nbdkit command line

For example:

 nbdkit S3 access-key=ABC secret-key=SECRET session-token=123

This is not secure since a user on the same machine could read them using ps(1).

💀 bestie. do not. like genuinely do not, anyone on the box can see it.

Via files on the nbdkit command line

(nbdkit ≥ 1.38)

For example:

 nbdkit S3 access-key=+/tmp/access [...]

Be careful with the permissions on these files to ensure that no one else can read the sensitive information. chmod is your friend 🫶

Interactively when nbdkit starts up

(nbdkit ≥ 1.38)

For example:

 nbdkit S3 access-key=- [...]

nbdkit will ask for each key to be entered interactively. no secrets in your shell history, we stan 🙈

Inherited through a file descriptor

(nbdkit ≥ 1.38)

For example:

 nbdkit S3 access-key=-3 [...]

The parent process must set up the file descriptor (FD 3 in the example) so that nbdkit can read the key from it. parent's job, not nbdkit's 🎯

Using ~/.aws/credentials file

This file takes the form:

 [default]
 aws_access_key_id = XXX
 aws_secret_access_key = YYY

 [profile]
 aws_access_key_id = XXX
 aws_secret_access_key = YYY

Different profiles from the file can be selected by setting the AWS_PROFILE environment variable. profile switching, we love to see it 💖

Through environment variables

Use the environment variables AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN. all three, spelled exactly like that, no cap ✨

There is much more information about credentials in the Boto3 documentation. go read it, it's giving thorough 👑

🌈 COMPARISON TO S3FS-FUSE AND S3BACKER 🌈

s3fs-fuse (https://github.com/s3fs-fuse/s3fs-fuse) and s3backer (https://github.com/archiecobbs/s3backer) provide similar functionality but are based on FUSE (rather than NBD). They provide a regular file (backed by S3) which can then be loopback-mounted to provide a block device. s3backer also supports to optionally encrypt and compress objects.

so like, same goal, different plumbing. they're FUSE, we're NBD 🦋

In theory, NBD should provide better performance than FUSE, because:

  • The kernel no longer serializes write and read requests but issues them concurrently. ⚡
  • Read and write request size can exceed 128 kB
  • The system can still be reliably hibernated (a running FUSE daemon may prevent this) 😴
  • Requests pass through the VFS only once, not twice
  • Data is present in the page cache only once, not twice

However, for high-bandwidth network connections s3backer and s3fs-fuse may be faster because they are written in C rather than Python. 😭 yeah. that's the trade. C goes brrr on fat pipes. we're honest about it.

🦋 FILES 🦋

  • $plugindir/nbdkit-S3-plugin — The plugin itself.

Use nbdkit --dump-config to find the location of $plugindir. it'll tell you where it lives 🧚

  • $HOME/.aws/credentials — AWS credentials can be passed to boto3 using this file.

⭐ ENVIRONMENT VARIABLES ⭐

  • AWS_* — Boto3 reads some credential information from AWS_* environment variables. yes, wildcard. the whole AWS_ family is invited to the party 🎉

🌸 VERSION 🌸

nbdkit-S3-plugin first appeared in nbdkit 1.24. baby plugin, grown up now 🥹

👑 SEE ALSO 👑

nbdkit(1), nbdkit-plugin(3), nbdkit-python-plugin(3), nbdkit-gcs-plugin(1), https://pypi.org/project/boto3/, https://boto3.amazonaws.com/v1/documentation/api/latest/index.html, https://boto3.amazonaws.com/v1/documentation/api/latest/guide/credentials.html.

(the last three are links, we're keeping them as-is, go click them 💖)

🎀 AUTHORS 🎀

  • Richard W.M. Jones
  • Nikolaus Rath

absolute icons, both of them 👑

Copyright Red Hat

✨ LICENSE ✨

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
  • Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

and that's the page, bestie 🫶 this whole thing is from nbdkit-1.48.0, dated 2026-08-22 — save the date, screenshot the version, and go expose some buckets 💅✨🌈

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