3 nbdkit-cacheextents-filter - cache extents
7 nbdkit --filter=cacheextents plugin
11 C<nbdkit-cacheextents-filter> is a filter that caches the result of last
14 A common use for this filter is to improve performance when using a
15 client performing a linear pass over the entire image while asking for
16 only one extent at a time (such as S<C<qemu-img convert>>), but where
17 the plugin can provide multiple extents for the same high latency as a
18 single extent (such as L<nbdkit-vddk-plugin(1)>). For example:
20 nbdkit -U - --filter=cacheextents --run 'qemu-img map $nbd' vddk ...
22 For files with big extents (when it is unlikely for one extents() call
23 to return multiple different extents) this does not slow down the
26 This filter only caches image metadata; to also cache image contents,
27 place this filter between L<nbdkit-cache-filter(1)> and the plugin.
31 There are no parameters specific to nbdkit-cacheextents-filter. Any
32 parameters are passed through to and processed by the underlying
33 plugin in the normal way.
39 =item F<$filterdir/nbdkit-cacheextents-filter.so>
43 Use C<nbdkit --dump-config> to find the location of C<$filterdir>.
49 C<nbdkit-cacheextents-filter> first appeared in nbdkit 1.14.
54 L<nbdkit-cache-filter(1)>,
55 L<nbdkit-extentlist-filter(1)>,
56 L<nbdkit-readahead-filter(1)>,
57 L<nbdkit-scan-filter(1)>,
58 L<nbdkit-vddk-plugin(1)>,