Block device compression with the cloop module
DEEP COMPRESSION
The cloop module lets you manage compression at the block device level. Read on to learn how Knoppix and other Live CDs fit all that software on a single disc.
Cloop is a kernel block device module used in Live CDs such as Knoppix. The cloop module allows the system to read compressed data, usually from a file, thus creating compressed virtual disks. Using cloop, a Linux installation of about 2GB fits on a single 700MB CD-R disc. In this article, I look at how cloop works and provide some insight into general kernel structures of a block device. A Unix system traditionally distinguishes between character-based and block-based devices. If you look into the output of ls -l /dev, you will easily recognize these devices by the prefix – c for character-based and b for block-based devices – at the beginning of the output line (see Listing 1).