geom_uzip — GEOM based compressed disk images and partitions

       The  geom_uzip  driver was written by Max Khon <fjoe@FreeBSD.org>.  The block de-duplication code as well
       as some geom_uzip driver optimizations have been contributed by Maxim Sobolev <sobomax@FreeBSD.org>.  The
       LZMA decompression support and CLOOP 3.0 support have been added by Aleksandr Rybalko <ray@FreeBSD.org>.

       This manual page was written by Ceri Davies <ceri@FreeBSD.org>.

Debian                                          February 26, 2019                                   GEOM_UZIP(4)

       The  geom_uzip  framework provides support for compressed read-only disk images.  This allows significant
       storage savings at the expense of a some CPU time on each read.  Data written  in  the  GEOM  label  area
       allows  geom_uzip to detect compressed images which have been created with mkuzip(8) and presented to the
       kernel as a logical disk device via md(4).  geom_uzip creates a unique md#.uzip device for each image.

       geom_uzip is not limited to supporting only md(4) images.  The image can also reside on a  block  device.
       (For  example,  a  disk, USB flash drive, DVD-ROM, etc.) The appropriate device node will appear with the
       .uzip suffix.

             # gpart show da0
             =>      0  7833600  da0  BSD  (3.7G)
                     0  2097152    1  freebsd-ufs  (1.0G)
               2097152  5736448       - free -  (2.7G)
             # gpart add -t freebsd-ufs -s 1G da0
             da0b added
             # dd if=/tmp/20160217_dcomp_zcomp.uzip bs=256k of=/dev/da0b
             3190+1 records in
             3190+1 records out
             836331008 bytes transferred in 111.021489 secs (7533055 bytes/sec)
             # fsck -t ffs /dev/da0b.uzip
             ** /dev/da0b.uzip (NO WRITE)
             ** Last Mounted on /mnt
             ** Phase 1 - Check Blocks and Sizes
             ** Phase 2 - Check Pathnames
             ** Phase 3 - Check Connectivity
             ** Phase 4 - Check Reference Counts
             ** Phase 5 - Check Cyl groups
             97455 files, 604242 used, 184741 free (2349 frags, 22799 blocks,
                0.3% fragmentation)
             # mount -o ro /dev/da0b.uzip /mnt
             # df /dev/da0b.uzip
             Filesystem     1K-blocks    Used  Avail Capacity  Mounted on
             /dev/da0b.uzip   3155932 2416968 738964    77%    /mnt

       The geom_uzip device is subsequently used by  FreeBSD  kernel  to  access  the  uncompressed  data.   The
       geom_uzip  driver  does  not  allow  write  operations  to  the  underlying  disk  image.  To check which
       “providers” match a given geom_uzip device:

             # geom uzip list
             Geom name: md1.uzip
             Providers:
             1. Name: md1.uzip
                Mediasize: 22003712 (21M)
                Sectorsize: 512
             Consumers:
             1. Name: md1
                Mediasize: 9563648 (9.1M)
                Sectorsize: 512

             Geom name: da0b.uzip
             Providers:
             1. Name: da0b.uzip
                Mediasize: 3355443200 (3.1G)
                Sectorsize: 512
             Consumers:
             1. Name: da0b
                Mediasize: 1073741824 (1.0G)
                Sectorsize: 512

       geom_uzip allows mounting the  root  file  system  from  a  compressed  disk  partition  by  setting  the
       vfs.root.mountfrom tunable.  See loader.conf(5) for details.

       Several  flags  are  provided  for  tracing  geom_uzip  I/O  operations and TOC parsing via the following
       sysctls.

       kern.geom.uzip.debug
               Log level.  Zero  disables  logging.   Higher  values  enable  more  verbose  debug  logging  for
               geom_uzip.  Supported levels are from 0 (no logging) to 4 (maximum amount of logging).

       kern.geom.uzip.debug_block
               Log operations involving compressed cluster number.

       geom_uzip — GEOM based compressed disk images and partitions

GEOM(4), md(4), geom(8), mkuzip(8)

       To compile this driver into the kernel, place the following line in your kernel configuration file:

             devicexzoptionsGEOM_UZIP

       Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

             geom_uzip_load="YES"