nbdkit-cacheextents-filter man page

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

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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.

Referenced By

nbdkit(1), nbdkit-cache-filter(1), nbdkit-extentlist-filter(1), nbdkit-filter(3), nbdkit-release-notes-1.14(1).

2020-03-20 nbdkit-1.19.4 NBDKIT