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nbdkit-readahead-filter(1)	    NBDKIT	    nbdkit-readahead-filter(1)

NAME
       nbdkit-readahead-filter - prefetch data when reading sequentially

SYNOPSIS
	nbdkit --filter=readahead plugin

DESCRIPTION
       "nbdkit-readahead-filter" is a filter that prefetches data when the
       client is reading sequentially.

       A common	use for	this filter is to accelerate sequential	copy
       operations (like	"qemu-imgA convert") when plugin requests have a high
       overhead	(like nbdkit-curl-plugin(1)).  For example:

	nbdkit -U - --filter=readahead curl https://example.com/disk.img \
	       --run 'qemu-img convert $nbd disk.img'

       The filter uses a simple	adaptive algorithm which accelerates
       sequential reads, but has a small penalty if the	client does random
       reads.  If the client mixes reads with writes or	write-like operations
       (trimming, zeroing) then	it will	work but there can be a	large
       performance penalty.

PARAMETERS
       There are no parameters specific	to nbdkit-readahead-filter.  Any
       parameters are passed through to	and processed by the underlying	plugin
       in the normal way.

FILES
       $filterdir/nbdkit-readahead-filter.so
	   The filter.

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

VERSION
       "nbdkit-readahead-filter" first appeared	in nbdkit 1.12.

SEE ALSO
       nbdkit(1), nbdkit-cache-filter(1), nbdkit-curl-plugin(1),
       nbdkit-retry-filter(1), nbdkit-ssh-plugin(1), nbdkit-vddk-plugin(1),
       nbdkit-filter(3), qemu-img(1).

AUTHORS
       Richard W.M. Jones

COPYRIGHT
       Copyright (C) 2019 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:

       o   Redistributions of source code must retain the above	copyright
	   notice, this	list of	conditions and the following disclaimer.

       o   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.

       o   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.

       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.

nbdkit-1.20.4			  2020-08-28	    nbdkit-readahead-filter(1)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | FILES | VERSION | SEE ALSO | AUTHORS | COPYRIGHT | LICENSE

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