nbdkit-xz-plugin(1)

1nbdkit-xz-plugin(1)                 NBDKIT                 nbdkit-xz-plugin(1)
2
3
4

NAME

6       nbdkit-xz-plugin - nbdkit xz plugin
7

SYNOPSIS

9        nbdkit xz [file=]FILENAME.xz
10

DEPRECATED

12       The xz plugin is deprecated in nbdkit ≥ 1.9.2 and will be removed in
13       nbdkit 1.12.  It has been replaced with a filter with the same
14       functionality, see nbdkit-xz-filter(1).  You can use the filter like
15       this:
16
17        nbdkit --filter=xz file file.xz
18

DESCRIPTION

20       "nbdkit-xz-plugin" is a file serving plugin for nbdkit(1).
21
22       It serves the named "FILENAME.xz" over NBD, uncompressing it on the
23       fly.  The plugin only supports read-only connections.
24
25   GETTING BEST RANDOM ACCESS PERFORMANCE FROM XZ
26       xz(1) files are split into streams and blocks.  Most xz files contain
27       only one stream which contains one or more blocks.  You can find out
28       how many streams and blocks are in an xz file by doing:
29
30        $ xz --list winxp.img.xz
31        Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
32            1       1  2,100.0 MiB  6,144.0 MiB  0.342  CRC64   winxp.img.xz
33           ↑↑↑     ↑↑↑
34         streams  blocks
35
36       xz files are seekable on block boundaries only.  Seeking is done by
37       seeking directly to the lower block boundary, then uncompressing data
38       until the precise byte is reached.  As uncompressing xz data is slow,
39       to get best random access performance, you must prepare your xz files
40       with many small blocks.
41
42       Use the --block-size option with a small-ish block size.  For example
43       this is the same image compressed with a 16 MB block size:
44
45        $ xz --best --block-size=16777216 winxp.img
46                    ─────────────────────
47        $ xz --list winxp.img.xz
48        Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
49            1     384  2,120.1 MiB  6,144.0 MiB  0.345  CRC64   winxp.img.xz
50                  ↑↑↑
51                 blocks
52
53       This file can be accessed randomly.  At most 16 MB will have to be
54       uncompressed to seek to any byte.
55
56       As you would expect, xz cannot compress as efficiently when using a
57       smaller block size.  The space penalty in the above example is < 1% of
58       the compressed file size.
59

PARAMETERS

61       [file=]FILENAME.xz
62           Serve the file named "FILENAME.xz".
63
64           This parameter is required.
65
66           "file=" is a magic config key and may be omitted in most cases.
67           See "Magic parameters" in nbdkit(1).
68
69       maxblock=SIZE
70           The maximum block size that the plugin will read.  The plugin will
71           refuse to read xz files that contain any block larger than this
72           size.
73
74           See the discussion above about creating xz files with small block
75           sizes in order to reduce memory usage and increase performance.
76
77           This parameter is optional.  If not specified it defaults to 512M.
78
79       maxdepth=N
80           Maximum number of blocks stored in the LRU block cache.
81
82           This parameter is optional.  If not specified it defaults to 8.
83
84           The plugin may allocate up to maximum block size in file * maxdepth
85           bytes of memory per connection.
86

AUTHORS

91       Richard W.M. Jones
92

COPYRIGHT

94       Copyright (C) 2013 Red Hat Inc.
95

LICENSE

97       Redistribution and use in source and binary forms, with or without
98       modification, are permitted provided that the following conditions are
99       met:
100
101       ·   Redistributions of source code must retain the above copyright
102           notice, this list of conditions and the following disclaimer.
103
104       ·   Redistributions in binary form must reproduce the above copyright
105           notice, this list of conditions and the following disclaimer in the
106           documentation and/or other materials provided with the
107           distribution.
108
109       ·   Neither the name of Red Hat nor the names of its contributors may
110           be used to endorse or promote products derived from this software
111           without specific prior written permission.
112
113       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
114       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
115       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
116       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
117       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
118       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
119       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
120       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
121       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
122       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
123       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
124
125
126
127nbdkit-1.11.11                    2019-03-29               nbdkit-xz-plugin(1)