Block device compression with the cloop module


Article from Issue 86/2008

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).

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