NAME

       create_compressed_fs,  extract_compressed_fs  - convert and extract a filesystem to/from a
       cloop volume

SYNOPSIS

       create_compressed_fs [ OPTIONS ] image outfile

       extract_compressed_fs filename

DESCRIPTION

       create_compressed_fs compresses a filesystem image to  a  compressed  image  suitable  for
       mounting with the cloop driver.

       extract_compressed_fs uncompresses a filesystem image created by create_compressed_fs.

OPTIONS

       Run  the  create_compressed_fs  command  with  "-h" to get a list of available options and
       description of data storages modes and  advanced  usage  (eg.  with  a  network  cluster).
       Blocksize must be a multiple of 512 bytes.

       There  is  an  alternative  set  of  options which is supported for compatibility with the
       original version of create_compressed_fs. When it's called with a pure number  as  output,
       it  assumes  the old syntax and maps the default options to memory mode and the block size
       to the number. -b for best mode is recognized as well.

EXAMPLES

       create_compressed_fs image.ext2 image.ext2.cloop

       extract_compressed_fs image.ext2.cloop | cmp image.ext2 -

       mkcmd="genisoimage -joliet-long -D -r data"

       $mkcmd | create_compressed_fs -s $($mkcmd --print-size)i - file.cloop

       create_compressed_fs image.iso -S image.cloop.a0 - | split -b 1024m - image.cloop.

       cat image.cloop.* | cdrskin -

NOTES

       For optimal performance, create_compressed_fs should be used with real  input  and  output
       files.

       Operation  with  STDIN  or STDOUT is complicated. create_compressed_fs cannot operate as a
       simple pipe filter because it needs to know some things in advance: a) the data length, b)
       the  block lengths calculated during the compression. This meta data needs to be stored in
       the header AFTER the compression is trough, therefore it  is  not  possible  to  push  all
       generated data to STDOUT on-the-fly.

       And  so  compromises  need  to  be  made.  The  simpliest  method  (used  by  the  ancient
       create_compressed_fs) is a big temporary memory buffer (option -m) to keep compressed data
       in RAM. However, the overall system performance suffers from such usage and this may drive
       other applications into OOM conditions.

       The next alternative to this is storing the temprorary data in an extra file aside (the -f
       option).  This  improves the overall system performance but create_compressed_fs operation
       is slower because it needs to copy data back when it's finished. Plus, double  disk  space
       for the output is required. If disk space is limited, the -r option could be used (reusing
       output file for temporary data), however the speed of  the  copy-back  step  may  decrease
       significantly.

       There  are  strategies  to avoid the temporary data storage completely.  First, only files
       should be used. If that is not possible, then the output should be a (seekable)  file  and
       the  input  data  length  should be known (either specified with the -s option or detected
       from the input file size).

       Second, it is possible to store the header of the cloop volume in a separate  file.  After
       the work, header can be merged together with the compressed data with the cat command. The
       output data can be written to stdout. Since the header is stored too late, this method  is
       not  very  usefull for immediate data transfer.  However, it allows to do some tricks like
       piping to the split utility (to store DVD images in smaller files on VFAT) or piping  data
       trough ssh if the local system has no disk space (and copying the header separately).

MOUNTING

       You  can  pass  an  option  to  the  cloop  module  on  loading, or use losetup or losetup
       functionality of the mount command. Examples:

       insmod cloop.o file=/path/to/compressed/image

       losetup /dev/cloop1 /path/to/compressed/image

       mount -o ro -t whatever /dev/cloop /mnt/compressed

       mount cl /mnt/misc -oloop=/dev/cloop0

SEE ALSO

       /usr/share/doc/cloop-utils/*, /usr/share/doc/cloop-src/*

AUTHOR

       This manual page was written by Eduard Bloch <blade@debian.org> for the  Debian  GNU/Linux
       system  (but  may  be  used  by others).  Permission is granted to copy, distribute and/or
       modify this document under the terms of the GNU GPLv2.

                                         04 Dezember 2006                 CREATE_COMPRESSED_FS(1)