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.IX Title "nbdkit-sparse-random-plugin 1"
.TH nbdkit-sparse-random-plugin 1 2024-04-21 nbdkit-1.38.1 NBDKIT
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
nbdkit\-sparse\-random\-plugin \- make sparse random disks
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 3
\& nbdkit sparse\-random [size=]SIZE [seed=SEED]
\&                      [percent=N] [runlength=N]
\&                      [random\-content=true]
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-sparse\-random\-plugin\*(C'\fR is a plugin for \fBnbdkit\fR\|(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 \fBnbdcopy\fR\|(1).  To get a
non-sparse random disk, see \fBnbdkit\-random\-plugin\fR\|(1).
.PP
The size of the virtual disk must be specified using the \f(CW\*(C`size\*(C'\fR
parameter.  If you specify the \f(CW\*(C`seed\*(C'\fR parameter then you will get the
same random data over multiple runs with the same seed.
.PP
The \f(CW\*(C`percent\*(C'\fR parameter controls the percentage of the disk which
contains random data versus sparse empty space.
.PP
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
\&\f(CW\*(C`runlength\*(C'\fR parameter controls the average length of each run of
random data.
.PP
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 \f(CW\*(C`random\-content=true\*(C'\fR.  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 \fInot\fR cryptographically secure.
.SS "Writes and testing copying"
.IX Subsection "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:
.PP
.Vb 1
\& nbdkit sparse\-random size=1T \-\-run \*(Aqnbdcopy "$uri" "$uri"\*(Aq
.Ve
.PP
\&\f(CW\*(C`qemu\-img convert\*(C'\fR could be used in place of nbdcopy.
See also \fBnbdkit\-checkwrite\-filter\fR\|(1).
.SH PARAMETERS
.IX Header "PARAMETERS"
.IP \fBpercent=\fRN 4
.IX Item "percent=N"
Specify the approximate percentage of the disk which contains random
data versus sparse empty space.  The default is 10 (10%).
\&\f(CW\*(C`percent=0\*(C'\fR will create a completely empty disk and \f(CW\*(C`percent=100\*(C'\fR
will create a completely full disk.
.IP \fBrandom\-content=true\fR 4
.IX Item "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.
.IP \fBrunlength=\fRN 4
.IX Item "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.
.IP \fBseed=\fRSEED 4
.IX Item "seed=SEED"
Specify the random seed to get repeatable data over multiple runs.
.Sp
If not specified then a random seed is chosen.
.IP [\fBsize=\fR]SIZE 4
.IX Item "[size=]SIZE"
Specify the virtual size of the disk image.
.Sp
This parameter is required.
.Sp
\&\f(CW\*(C`size=\*(C'\fR is a magic config key and may be omitted in most cases.
See "Magic parameters" in \fBnbdkit\fR\|(1).
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$plugindir\fR\fI/nbdkit\-sparse\-random\-plugin.so\fR 4
.el .IP \fR\f(CI$plugindir\fR\fI/nbdkit\-sparse\-random\-plugin.so\fR 4
.IX Item "$plugindir/nbdkit-sparse-random-plugin.so"
The plugin.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$plugindir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-sparse\-random\-plugin\*(C'\fR first appeared in nbdkit 1.24.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-plugin\fR\|(3),
\&\fBnbdkit\-data\-plugin\fR\|(1),
\&\fBnbdkit\-full\-plugin\fR\|(1),
\&\fBnbdkit\-null\-plugin\fR\|(1),
\&\fBnbdkit\-ones\-plugin\fR\|(1),
\&\fBnbdkit\-pattern\-plugin\fR\|(1),
\&\fBnbdkit\-random\-plugin\fR\|(1),
\&\fBnbdkit\-zero\-plugin\fR\|(1),
\&\fBnbdcopy\fR\|(1),
\&\fBqemu\-img\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
.IP \(bu 4
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.
.PP
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.