1nbdkit-cacheextents-filter(1)       NBDKIT       nbdkit-cacheextents-filter(1)
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NAME

6       nbdkit-cacheextents-filter - cache extents
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SYNOPSIS

9        nbdkit --filter=cacheextents plugin
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DESCRIPTION

12       "nbdkit-cacheextents-filter" is a filter that caches the result of last
13       extents() call.
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15       A common use for this filter is to improve performance when using a
16       client performing a linear pass over the entire image while asking for
17       only one extent at a time (such as "qemu-img convert"), but where the
18       plugin can provide multiple extents for the same high latency as a
19       single extent (such as nbdkit-vddk-plugin(1)).  For example:
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21        nbdkit -U - --filter=cacheextents --run 'qemu-img map $nbd' vddk ...
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23       For files with big extents (when it is unlikely for one extents() call
24       to return multiple different extents) this does not slow down the
25       access.
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27       This filter only caches image metadata; to also cache image contents,
28       place this filter between nbdkit-cache-filter(1) and the plugin.
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PARAMETERS

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

36       $filterdir/nbdkit-cacheextents-filter.so
37           The filter.
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39           Use "nbdkit --dump-config" to find the location of $filterdir.
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VERSION

42       "nbdkit-cacheextents-filter" first appeared in nbdkit 1.14.
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SEE ALSO

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

50       Martin Kletzander
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53       Copyright (C) 2019 Red Hat Inc.
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LICENSE

56       Redistribution and use in source and binary forms, with or without
57       modification, are permitted provided that the following conditions are
58       met:
59
60       ·   Redistributions of source code must retain the above copyright
61           notice, this list of conditions and the following disclaimer.
62
63       ·   Redistributions in binary form must reproduce the above copyright
64           notice, this list of conditions and the following disclaimer in the
65           documentation and/or other materials provided with the
66           distribution.
67
68       ·   Neither the name of Red Hat nor the names of its contributors may
69           be used to endorse or promote products derived from this software
70           without specific prior written permission.
71
72       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
73       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
74       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
75       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
76       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
77       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
78       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
79       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
80       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
81       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
82       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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86nbdkit-1.18.4                     2020-04-16     nbdkit-cacheextents-filter(1)
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