1 .\" ----------------------------------------------------------------------------
2 .\" "THE BEER-WARE LICENSE" (Revision 42):
3 .\" <sobomax@FreeBSD.ORG> wrote this file. As long as you retain this notice you
4 .\" can do whatever you want with this stuff. If we meet some day, and you think
5 .\" this stuff is worth it, you can buy me a beer in return. Maxim Sobolev
6 .\" ----------------------------------------------------------------------------
15 .Nd compress disk image for use with
22 .Op Fl s Ar cluster_size
27 utility compresses a disk image file so that the
29 class will be able to decompress the resulting image at run-time.
30 This allows for a significant reduction of size of disk image at
31 the expense of some CPU time required to decompress the data each
41 image is split into clusters; each cluster is compressed using
44 The resulting set of compressed clusters along with headers that allow
45 locating each individual cluster is written to the output file.
49 .Bl -tag -width indent
51 Name of the output file
53 The default is to use the input name with the suffix
55 .It Fl s Ar cluster_size
56 Split the image into clusters of
58 bytes, 16384 bytes by default.
61 should be a multiple of 512 bytes.
63 Display verbose messages.
66 The compression ratio largely depends on the cluster size used.
67 .\" The following two sentences are unclear: how can gzip(1) be
68 .\" used in a comparable fashion, and wouldn't a gzip-compressed
69 .\" image suffer from larger cluster sizes as well?
70 For large cluster sizes (16K and higher), typical compression ratios
71 are only 1-2% less than those achieved with
73 However, it should be kept in mind that larger cluster
74 sizes lead to higher overhead in the
76 class, as the class has to decompress the whole cluster even if
77 only a few bytes from that cluster have to be read.
82 inserts a short shell script at the beginning of the generated image,
83 which makes it possible to
85 the image just like any other shell script.
86 The script tries to load the
88 class if it is not loaded, configure the image as an
92 and automatically mount it using
94 on the mount point provided as the first argument to the script.
106 .An Maxim Sobolev Aq sobomax@FreeBSD.org