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


       create_compressed_fs [ OPTIONS ] image outfile

       extract_compressed_fs filename


       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


       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

       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.


       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 -

       cat image.cloop.* | cdrecord -


       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).


       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


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


       This manual page was written by Eduard Bloch <> 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)