GEOM_UZIP(4) FreeBSD Kernel Interfaces Manual GEOM_UZIP(4)
NAME
geom_uzip - GEOM based compressed disk images and partitions
SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
device xz
options zstd
options GEOM_UZIP
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
geom_uzip_load="YES"
DESCRIPTION
The geom_uzip framework provides support for compressed read-only disk
images. This allows significant storage savings at the expense of 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.
DIAGNOSTICS
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.
SEE ALSO
GEOM(4), md(4), geom(8), mkuzip(8)
HISTORY
Zstd support was added in FreeBSD 13.0.
AUTHORS
The geom_uzip driver was written by Max Khon <
[email protected]>. The
block de-duplication code as well as some geom_uzip driver optimizations
have been contributed by Maxim Sobolev <
[email protected]>. The LZMA
decompression support and CLOOP 3.0 support have been added by Aleksandr
Rybalko <
[email protected]>.
This manual page was written by Ceri Davies <
[email protected]>.
FreeBSD 14.1-RELEASE-p8 April 28, 2021 FreeBSD 14.1-RELEASE-p8