nbdkit-memory-plugin man page

nbdkit-memory-plugin — nbdkit virtual memory plugin

Synopsis

 nbdkit memory size=SIZE

Description

"nbdkit-memory-plugin" is a plugin for nbdkit(1) which stores a single disk image in virtual memory, and discards it when nbdkit exits.  This plugin can be used for testing or where you don't care about the final content of the disk image.

All nbdkit clients will see the same disk content, initially all zeroes.

The disk image is stored in memory using a sparse array.  The allocated parts of the disk image cannot be larger than physical RAM plus swap, less whatever is being used by the rest of the system.  If you want to allocate more space than this use nbdkit-file-plugin(1) backed by a temporary file instead.

However the virtual size can be as large as you like, up to the maximum supported by nbdkit (2⁶³-1 bytes).  This limit is tested when nbdkit is compiled, and it should work on all platforms and architectures supported by nbdkit.

Preloading small amounts of data

If you want an in-memory disk image preinitialized with a small amount of data specified on the command line, look at nbdkit-data-plugin(1) instead.  Note by "small" this does not mean that the virtual disk image must be small, but that the amount of data initially stored sparsely is small enough to specify on the command line.

Preloading large amounts of data

If you want to preload a large amount of data (eg. a disk image) into the memory plugin, use qemu-img(1):

 $ rm -f pid
 $ nbdkit -P pid memory size=10G
 
 # wait for nbdkit to become ready to accept connections:
 $ while [ ! -f pid ]; do sleep 1; done
 
 # preload Fedora disk image:
 $ virt-builder fedora-28 --size=10G
 $ qemu-img convert -p -n fedora-28.img nbd:localhost:10809

Parameters

size=SIZE

Specify the virtual size of the disk image.

This parameter is required.

See Also

nbdkit(1), nbdkit-plugin(3), nbdkit-data-plugin(1), nbdkit-file-plugin(1).

Authors

Richard W.M. Jones

License

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

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.

Referenced By

nbdkit(1), nbdkit-data-plugin(1), nbdkit-loop(1), nbdkit-plugin(3).

2018-12-04 nbdkit-1.9.4 NBDKIT