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     geom_uncompress — GEOM based compressed disk images


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

           options GEOM_UNCOMPRESS

     Alternatively, to load the driver as a module at boot time, place the following line in



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

     The geom_uncompress device is subsequently used by the FreeBSD kernel to access the disk
     images.  The geom_uncompress driver does not allow write operations to the underlying disk
     image.  To check which md(4) devices match a given geom_uncompress device:

           # geom uncompress list
           Geom name: md0.uncompress
           1. Name: md0.uncompress
              Mediasize: 52428800 (50M)
              Sectorsize: 512
              Mode: r1w0e0
           1. Name: md0
              Mediasize: 20864000 (20M)
              Sectorsize: 512
              Mode: r1w0e0


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


     The geom_uncompress driver was written by Maxim Sobolev <> and Aleksandr
     Rybalko <>.  This manual page was written by Luiz Otavio O Souza