DOKK / manpages / debian 11 / nbdkit / nbdkit-sparse-random-plugin.1.en
nbdkit-sparse-random-plugin(1) NBDKIT nbdkit-sparse-random-plugin(1)

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

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

"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 random data is generated using an insecure method.

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).

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.
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.
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).

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

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

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

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).

Richard W.M. Jones

Copyright (C) 2018 Red Hat Inc.

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2021-01-20 nbdkit-1.24.1