Reference

geom_uncompress(4freebsd)

GEOM based compressed disk images

NAME

geom_uncompress – GEOM based compressed disk images

SYNOPSIS

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 loader.conf(5):

geom_uncompress_load="YES"

DESCRIPTION

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
Providers:
1. Name: md0.uncompress
   Mediasize: 52428800 (50M)
   Sectorsize: 512
   Mode: r1w0e0
Consumers:
1. Name: md0
   Mediasize: 20864000 (20M)
   Sectorsize: 512
   Mode: r1w0e0

SEE ALSO

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

AUTHORS

The geom_uncompress driver was written by Maxim Sobolev ⟨[email protected]⟩ and Aleksandr Rybalko ⟨[email protected]⟩. This manual page was written by Luiz Otavio O Souza ⟨[email protected]⟩.