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

49       Martin Kletzander
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52       Copyright (C) 2019 Red Hat Inc.
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LICENSE

55       Redistribution and use in source and binary forms, with or without
56       modification, are permitted provided that the following conditions are
57       met:
58
59       ·   Redistributions of source code must retain the above copyright
60           notice, this list of conditions and the following disclaimer.
61
62       ·   Redistributions in binary form must reproduce the above copyright
63           notice, this list of conditions and the following disclaimer in the
64           documentation and/or other materials provided with the
65           distribution.
66
67       ·   Neither the name of Red Hat nor the names of its contributors may
68           be used to endorse or promote products derived from this software
69           without specific prior written permission.
70
71       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
72       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
73       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
74       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
75       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
76       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
77       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
78       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
79       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
80       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
81       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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85nbdkit-1.16.1                     2019-12-03     nbdkit-cacheextents-filter(1)
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