NAME

       nbdkit-sparse-random-plugin - make sparse random disks

SYNOPSIS

        nbdkit sparse-random [size=]SIZE [seed=SEED]
                             [percent=N] [runlength=N]
                             [random-content=true]

DESCRIPTION

       "nbdkit-sparse-random-plugin" is a plugin for nbdkit(1) which makes disks containing
       sparse blocks of random data.  These disks have a similar shape to virtual machine disks,
       and this plugin can be used to benchmark disk copying tools like nbdcopy(1).  To get a
       non-sparse random disk, see nbdkit-random-plugin(1).

       The size of the virtual disk must be specified using the "size" parameter.  If you specify
       the "seed" parameter then you will get the same random data over multiple runs with the
       same seed.

       The "percent" parameter controls the percentage of the disk which contains random data
       versus sparse empty space.

       The plugin does not generate random data spread evenly over the disk.  Instead to make it
       look more like a real virtual machine disk, it tries to create runs of data and runs of
       empty space.  The "runlength" parameter controls the average length of each run of random
       data.

       The data in each block normally consists of the same random non-zero byte repeated over
       the whole block.  If you want fully random content within each block use
       "random-content=true".  This is not the default because earlier testing of this plugin
       showed that a great deal of time was spent generating random content.  The random content
       is generated using a method which is not cryptographically secure.

   Writes and testing copying
       Writes to the disk verify that the data written is the same as the data read (if not,
       returning EIO).  Thus when testing copies you can use a single instance of this plugin for
       both read and write:

        nbdkit -U - sparse-random size=1T --run 'nbdcopy "$uri" "$uri"'

       "qemu-img convert" could be used in place of nbdcopy.  See also
       nbdkit-checkwrite-filter(1).

PARAMETERS

       percent=N
           Specify the approximate percentage of the disk which contains random data versus
           sparse empty space.  The default is 10 (10%).  "percent=0" will create a completely
           empty disk and "percent=100" will create a completely full disk.

       random-content=true
           By default a single random non-zero byte is repeated over the whole block, which is
           fast to generate and check.  If you want blocks where each byte is random, use this
           setting.

       runlength=N
           Specify the average length of runs of random data.  This is expressed in bytes and the
           usual modifiers can be used.  The default is 16M, meaning that (on average) data runs
           will be 16 megabytes in length.

       seed=SEED
           Specify the random seed to get repeatable data over multiple runs.

           If not specified then a random seed is chosen.

       [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).

FILES

       $plugindir/nbdkit-sparse-random-plugin.so
           The plugin.

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

VERSION

       "nbdkit-sparse-random-plugin" first appeared in nbdkit 1.24.

SEE ALSO

       nbdkit(1), nbdkit-plugin(3), nbdkit-data-plugin(1), nbdkit-full-plugin(1),
       nbdkit-null-plugin(1), nbdkit-pattern-plugin(1), nbdkit-random-plugin(1),
       nbdkit-zero-plugin(1), nbdcopy(1), qemu-img(1).

AUTHORS

       Richard W.M. Jones

COPYRIGHT

       Copyright Red Hat

LICENSE

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