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dfg2ext

Secure online defragmentation for ext2/3 filesystems

This is a custom project I’ve always run on my own. I was looking for a way to defrag ext3 filesystems without having to back-up/restore, to have online defragmentation. I found davl-tools, installed and after that had some serious bash scripting. This is the cumulative work of over 2 years. Since davl-tools works also for ext2 filesystems you can also defragment ext2 filesystems.

As of now, it’s available on github (“activedevel” directory contains latest version, “stable” the previous stable one).

Just run “sh dfg5004.sh” if you wish to have a fast help at hand. If you want to have more info, the scripts are heavily commented. You’ll find description for each function, complete changelog, todo list in dfg5004.sh and its sub-files.

Shortly:

  • the core approach is very simplicistic: generate a list of fragmented files, “cp file file.unfragmented && mv file.unfragmented file”; relies on the anti-fragmentation features of the filesystem (aka: “allocate contiguosly if I know the size”); this also allows to defragment opened/locked files (/lib/libc.so being my nightmare at first)
  • heavily relies on functions: less code, less bugs, more portability and speed (source files have been splitted to allow for clearer understanding)
  • some functions return error codes: if some critical function fails, script will stop without touching the affected area (=saving your data)
  • though disabled by default, md5-summing is implemented (available via commandline switch): avoids relocating modified data, you won’t lose your modified data
  • I’m a speed fanatic myself, I wanted the job done as fast as it could be done: functions and loops have been scheduled to provide minimum runtime overhead (=minimum time spent in non-useful/onetime jobs)
  • it needs davl-tools; I’m providing a new version through a custom ebuild, patched to generate only the strict minimum for the script to run (no block allocation status->no more “cat list | grep -v …”->huge speedups); I still need to rework the script to recognize the new version, though
  • some files will never be completely defragmented: this is due to the filesystem’s structure and security descriptors, for those files we can only try to minimize the fragments (implemented function)
  • allows user-set exclusions (per-partition): >~75Mb files will never get to 1 fragment and will waste a lot of script’s time when defragmenting, you can safely exclude them or the entire directory

Scripts

This is a simple list of scripts that I've written myself. They are proof-of-concepts or small utilities which I could not find elsewhere.