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This is a NBD server for OpenStack Object Storage (Swift)

tag: 0.9.5

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Swift NBD Server

This is a Network Block Device (NBD) server for OpenStack Object Storage (Swift).

Very often users want to run tools like rsync on top of Swift, but this is not possible because the object storage HTTP API can't provide a file system alike functionality. This project aims to support a block interface for the object storage via NBD.

How it Works

swiftnbd translates the NBD requests (read/write with offset and length) to Swift object operations, as displayed in the following picture:

Although this strategy may work with any block interface, NBD was chosen because of its simplicity. The NBD server can serve the blocks over the network, but is recommended that it is used locally. Because the communication with Swift will be the bottleneck, the possible overhead of NBD on localhost is expected to not be significant.

The block device can be used only by one location at once. When a client is connected to the server, the container used as storage is marked as locked by adding metadata information to the container until the client disconnects and the container can be unlocked.

The server implements the new version of the NBD protocol and nbd-client 3.1 or later is highly recommended. For older versions of the protocol (nbd-client <= 2.9.16), please use the swiftnbd 0.9.4.




  • Linux (or any platform with NBD client; nbd-client 3.1+ recommended)
  • Python 2.7 (or later; Python 3 not supported yet)
  • python-swiftclient
  • gevent

To install the software, run the following command:

python install

Alternatively you can install it with pip:

pip install swiftnbd


A container needs to be setup with swiftnbd-ctl to be used by the server. First create a secrets.conf file:

username = user
password = pass

Optionally an authurl token can be used to specify an authentication URL per container.

The default location for the secrets is /etc/swiftnbd/secrets.conf, and an alternative location can be provided using --secrets flag.

Then run the control tool with setup command using the container name as first parameter and the maximum number of objects you want to allocate as second parameter:

swiftnbd-ctl setup container-name number-of-objects

For example, to setup a 1GB storage in myndb0 container:

swiftnbd-ctl setup mynbd0 16384

By default the objects stored by the server are 64KB, so 16384 * 65536 is 1GB.

After the container is setup, it can be served with swiftnbd-server:


For debugging purposes the -vf flag is recommended (verbose and foreground).

The server implements a local cache that by default is limited to 64 MB per container. That value can be configured using the -c flag indicating the max amount of memory to be used (in MB).

Once the server is running, nbd-client can be used to create the block device (as root):

modprobe nbd
nbd-client -N container-name /dev/nbd0

Then /dev/nbd0 can be used as a regular block device, ie:

mkfs.ext3 /dev/nbd0
mount /dev/nbd0 /mnt

Before stopping the server, be sure you unmount the device and stop the NBD client:

umount /mnt
nbd-client -d /dev/nbd0

The server will export all the containers listed in the secrets file. The list of exported container can be verified with the NBD client -list option (version >= 3.1):

nbd-client -list

Please check --help for further details.

The control tool

siwftnbd-ctl is used to perform different maintenance operations on the containers. It communicates directly with the object storage (the NBD server is not used).

To obtain the details of the containers listed in the secrets file:

swiftnbd-ctl list -s

To setup a container:

swiftnbd-ctl setup container-name number-of-objects

A custom object size can be indicated with the --object-size flag (default is 65536).

To unlock a locked container:

swiftnbd-ctl unlock container-name

To download a container into a local disk image (the resulting disk image can be mounted using a loop device):

swiftnbd-ctl download container-name image-file.raw

To delete a container (all the objects in the container will be deleted before deleting the container):

swiftnbd-ctl delete container-name

Known issues and limitations

  • The default 64KB object size is a wild/random guess, other values could be better.
  • It can be used over the Internet but the performance is dependant on the bandwidth, so it's recommended that the storage is accessible via LAN (or same data center with 100 mbps or better).



Contact and support

The project website is at:



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