NAME

nbdkit-cacheextents-filter - cache extents

SYNOPSIS

 nbdkit --filter=cacheextents plugin

DESCRIPTION

"nbdkit-cacheextents-filter" is a filter that caches the result of last extents() call.

A common use for this filter is to improve performance when using a client performing a linear pass over the entire image while asking for only one extent at a time (such as "qemu-img convert"), but where the plugin can provide multiple extents for the same high latency as a single extent (such as nbdkit-vddk-plugin(1)). For example:

 nbdkit -U - --filter=cacheextents --run 'qemu-img map $nbd' vddk ...

For files with big extents (when it is unlikely for one extents() call to return multiple different extents) this does not slow down the access.

This filter only caches image metadata; to also cache image contents, place this filter between nbdkit-cache-filter(1) and the plugin.

PARAMETERS

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

FILES

$filterdir/nbdkit-cacheextents-filter.so

The filter.

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

VERSION

"nbdkit-cacheextents-filter" first appeared in nbdkit 1.14.

SEE ALSO

nbdkit(1), nbdkit-cache-filter(1), nbdkit-extentlist-filter(1), nbdkit-readahead-filter(1), nbdkit-vddk-plugin(1), nbdkit-filter(3), qemu-img(1).

AUTHORS

Martin Kletzander

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:

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