Saturday, June 19, 2010

Data recovery tutorial using Ubuntu Linux

I have an old hard disk with corrupt NTFS volumes and I want to recover the data. I'm not sure how the drives got corrupt but they cannot be fixed by chkdsk /f. Fortunately, there's a plethora of open source data recovery tools available. Two such tools are foremost and photorec which specialize in combing through hard drive partitions to recover files based on header information. They can even recover files after accidental reformatting.

Foremost is a tool originally developed by the U.S. Air Force and is available via sudo apt-get install foremost. It can recover common file types such as txt, jpg, avi, and etc.. Foremost was last updated in 2008 which means that its knowledge of file headers is, at best, two years dated.

Photorec is part of the testdisk suite and is available via sudo apt-get install testdisk. Testdisk is a tool that not only "tests your disk" but also rebuilds your partition table. This is the tool to use if your hard drive's master boot record or partition table is corrupt. Photorec, like testdisk, is a poorly named command-line tool. Like foremost, photorec recovers files (not just photos) based on file headers. In fact, photorec supports more file types and is more up-to-date than foremost, which is evident by the fact that I was able to recover more files with photorec than foremost.

The problem with both foremost and photorec is that they recover file content but not file names. So you end up with directories of randomly named files with only the file extension preserved. It's not ideal but it's still better than not having the data at all.

See also:

Saturday, June 5, 2010

Towards a Universal VM

Alex Buckley talks the features and progress that should make the JVM the universal run-time environment for languages. Interesting discussion in the talk include:
  • the distinction between the roles of the byte-code compiler and JVM compiler.
  • a high-level overview of how the JVM does method inline optimizations.
  • the introduction of dynamicinvoke in the new JVM.
The talk is normally 1-2 steps lower level than what software developers deal with on a day-to-day basis but nevertheless very understandable and useful to know.