LinLogFS -- A Log-Structured Filesystem For Linux

LinLogFS was formely known as dtfs.

(Name change to avoid conflicts with SCO's dtfs)

Latest Modification: June 25th, 2001 by Anton Ertl

Recent Changes:

Added link to LFS, and did some more changes too the "Related Information" section.
Some ideas for an log-structured file system that came out of the work on LinLogFS. It's probably best to implement them from scratch (or starting with ext2 or so) rather than trying to port LinLogFS forward to Linux 2.6 and then add these ideas.
The main part of LinLogFS is stalled (Christian Czezatke's job does not leave enough time). If you are interested in maintaining/extending it, please contact Anton Ertl.
David A. Gatwood wrote a Cleaner for LinLogFS.
Usenix Freenix 2000 Paper on LinLogFS (Overview, some idea sketches)
The LinLogFS Mailing List has had no on-topic traffic in the last few tears, so better avoid it.
Summary of new design ideas is now available from here
Work is now partly sponsored by xS+S, my employer
Linlog filesystems can now be created on glibc 2.1/gcc 2.95.2 systems (thanks to Al Styrsky)
Inode (De)allocation is now fully implemented (needs testing)
Adapted LinLogFS for Linux 2.2.14

Goal of the Project

The goal of the project is to implement a log-structured file system within the Linux 2.2.x kernels. LinLogFS has a filesystem-independent core that provides general services required for a log-structured file system and uses a "traditional" file system implementation to do the actual filesystem/VFS operations.

The tradtional file system of choice is currently Linux' ext2 file system.

Using the ext2 file system together with the log-structured core should both reduce the implementation work required to be done and facilitate the future maintainence of LinLogFS: Additions to the ext2 file system features should (hopefully) be easy to integrate into the LinLog file system too.

Status of the Project

Basic filesystem operations are almost done. You should be able to perform all filesystem operations on a LinLogFS filesystem. What does not work right now is:

You cannot put a swapfile on a LinLogFS partition. (More fundamental issue.)
O_SYNC support is still incomplete.
Due to a bug in the mkfs utility, LinLogFS is currently broken on Big Endian platforms (Sparc, PowerPC).
What is still badly missing is a working cleaner that reclaims free disk space. (started)

The LinLogFS "FAQ"

This page contains general information about what LinLogFS actually is, etc...

Download the current version of LinLogFS

LinLogFS is now quite easy to install. But be aware that LinLogFS is nevertheless not practially usable as long as the items listed above are still unresolved.

Current Design Issues

This page lists a number of topics that are currently considered for addition to LinLogFS. The list found on this page is mainly motivated by my experiences during the work on LinLogFS so far.

The LinLogFS Mailing List

There is now a mailing list for LinLogFS. Future versions of LinLogFS will be announced there. Click on the link above to get information on how to subscribe to this mailing list.

The LinLogFS Documentation Page

If you're interested in the internals of dtfs, having a look at this page is highly recommended. You'll find a postscript document outlining the design and the implementation of LinLogFS there. Furthermore, a few older (and partly outdated) LinLogFS-related documents/design considerations can be found there, too.

Progress Of The Project/Current Tasks

The LinLog changelog page can be found here.

Related Information

LFS, a log-structured file system for Linux with snapshots.
The kfs Homepage. Cornelius linLogFS"Kees" Cook has started a Linux Log--Structured Filesystem project before came to live. He has been very helpful in the early design stages of LinLogFS. Furthermore this page contains an excellent collection of links referring to log-structured filesystem issues.
The ext2 Homepage. This is the primary source of information about ext2, the standard Linux filesystem.
The Linux device file system is generally very usable and of particular interest for the LinLogFS implementation. devfs makes is possible to create a device file node for each filesystem snaphsot relatively easily. [In Linux-2.6 it is deprecated and superseded by the combination of sysfs and udev; it will go away eventually.]
The Linux LVM Project This is an implementation of a logical volume manager for Linux. An LVM allows you to create logical devices from many physical ones, resize the logical device etc... Using a log-structured filesystem you should be able to do things like resizing a logical device holding a filesystem without the need to re-format.
Drbd, a block device which is designed to build high availability clusters.
The Computer Language Department of the Vienna University of Technology is hosting a few Linux--related projects. Here is an overview of them.

!!! BEWARE Link--Section is still incomplete!

Christian Czezatke, email: czezatke@complang.tuwien.ac.at

Anton Ertl