NAME

       nbdkit-memory-plugin - nbdkit virtual memory (RAM disk) 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.

EXAMPLES

       Create a one gigabyte sparse RAM disk:

        nbdkit memory 1G

       If you want to loop mount the above disk, see nbdkit-loop(1).

       Create the largest possible RAM disk:

        nbdkit memory $(( 2**63 - 1 ))

PARAMETERS

       [size=]SIZE
           Specify the virtual size of the disk image.

           This parameter is required.

           "size=" is a magic config key and may be omitted in most cases.  See "Magic parameters" in nbdkit(1).

NOTES

   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 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

FILES

       $plugindir/nbdkit-memory-plugin.so
           The plugin.

           Use "nbdkit --dump-config" to find the location of $plugindir.

VERSION

       "nbdkit-memory-plugin" first appeared in nbdkit 1.2.

SEE ALSO

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

AUTHORS

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2017-2018 Red Hat Inc.

LICENSE

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

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           the following disclaimer.

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           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.

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