DBMODE(8)

NAME
dbmode - change compression algorithm on a "DouBle" compressed block device

SYNOPSIS
dbmode -p special [encoding] dbmode /dev/doubleN [encoding]

DESCRIPTION
dbmode is used to check or change the default compression algorithm on a compressed block device. dbmode comes in two flavors. In the first form (dbmode -p special), the default compression algorithm can be read or updated. special is a compressed block device or file, created by the mkdble command. Any change to the default algorithm becomes permanent and becomes effective as soon as the device is next mounted. In the second form, (dbmode /dev/doubleN) the current compression algorithm, can be read/updated on a mounted compressed device. Any change to the current algorithm immediately overrides the default value until the device is dismounted. When invoked with no argument on /dev/doubleN, dbmode will report the current compression algorithm, the size of the compressed device, the size of the DouBle device the free compressed space and the current mount flags. When the device is mounted with "mount -t dble", these flags will automatically be changed by the driver as free space decreases. These flags have the following meaning: 800 - Ask the ext2-fs to clear free blocks (less than 10% free space). 10 - Switch to synchronous mode (less than 5% free space). 400 - Files become read-only (less than 100KB free space). 80 - The whole ext2-fs becomes read-only (less than 50 KB free space).

OPTIONS

encoding
    change default (-p), or current compression algorithm for a compressed device to: 0 - no compression 1 - LZW algorithm 10 - predictor algorithm 11 - LZV algorithm. 12 - LZRW2 algorithm. 13 - LZRW3A algorithm.

NOTES
The default algorithm should not be changed on a mounted device. In versions < 0.3, LZV,LZRW2,LZRW3A used to have codes 102, 212 and 312 respectively. Versions 0.3 and 0.4 are backward compatible with these values.

SEE ALSO
dbmount(8),dbumount(8),mkdble(8),dbck(8)

AUTHORS
Jean-Marc Verbavatz <jmv@achaz.saclay.cea.fr> LZV was written by Hermann Vogt <herm@pirx.han.de> LZRW* was written by Ross Williams predictor was written by Dave Rand and last modified by Peter Trattler

DISCLAIMER
All the compression algorithms are patented in some countries. For more information, refer to the compression FAQ, posted regularly on "comp.compression".