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GEOM_UNCOMPRESS(4)
GEOM_UNCOMPRESS(4) FreeBSD Kernel Interfaces Manual GEOM_UNCOMPRESS(4)

NAME

geom_uncompressGEOM 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

AUTHORS

The geom_uncompress driver was written by Maxim Sobolev <sobomax@FreeBSD.org> and Aleksandr Rybalko <ray@FreeBSD.org>. This manual page was written by Luiz Otavio O Souza <loos@FreeBSD.org>.
January 9, 2014 FreeBSD