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When backups fail: Data recovery

Continuing on the path begun in the last two columns, this week we’re going to discuss data recovery.

Even with proper backup methods in place, data can be lost for a variety of reasons, including accidental deletion or loss between backups.

There are a number of ways to recover data from the types of media previously mentioned — magnetic, flash and optical. Before diving into recovery methods, we’ll first need some background on the methods employed by the various forms of storage.

Magnetic storage is the most popular, and in most cases the easiest for recovering lost data. By definition, magnetic storage uses different patterns of magnetization on a magnetic material to store data. This form of non-volatile memory uses read/write heads to alter the magnetic patterns.

Due in part to the file structures used by all popular operating systems (Windows, Mac, Linux), this process allows “deleted” data to be recovered with the right knowledge and software.

I use the term “deleted” loosely. Perhaps the better term is “hidden.” When you tell the operating system to delete a file, that file is removed from the file structure the operating system uses, but the actual data that constitutes said data remains perfectly intact until something else physically takes its place.

There are a vast number of data recovery tools out there for recovering files in this state. My favorite freeware utility for Windows systems is Recuva from Piriform.

Some of the better software recovery tools can be quite advanced, requiring intricate knowledge of file structures and systems. But they do allow recovery in the worst situations.

Flash media, just like magnetic, is a non-volatile storage which allows data recovery. Instead of using the magic of magnets to perform its storage voodoo, flash media is electrically erased and reprogrammed.

Similar to magnetic storage, any deleted information remains intact until overwritten by new information. Many applications that work on magnetic storage will also work on flash data recovery. Recuva is still highly recommended for Windows systems.

Optical storage, such as CDs or DVDs, gets to be tricky when it comes to data recovery. With CDs/DVDs, data is recorded, or “burned,” by making specific patterns of marks that can be read by a precisely focused laser light.

There are two types of CDs/DVDs. “Recordable” discs (CD-R/DVD-R) can be written to only once.

I fondly remember my mother referring to “new” CD-Rs in the early 1990s as “WORMs,” meaning “Write Once Read Many.”

Data on CD-R/DVD-Rs may never be deleted, but due to CD/DVD burning software, data can still be lost — or, more accurately — hidden. The built-in session explorer feature in many popular CD/DVD authoring programs can bring this data back to life.

CD-RW/DVD-RW discs can be erased and rewritten. As with other forms of storage, this doesn’t necessarily mean the data is gone for good. A “quick erase” only resets the file allocation table, which is like a road map to all the files on the disc. The physical information is still intact until overwritten. By far the best Windows utility for optical data recovery is IsoBuster.

Here’s an important thing to remember: Do not install data recovery software onto the same storage media from which you wish to recover data. Doing so could overwrite the very data you’re trying to rescue.

Bear in mind that physical damage is an entirely different story. If your hard drive is making funny noises, or your system seems to be freezing up during data recovery, stop immediately and seek professional help. Continuing to attempt data recovery in these situations can cause permanent data loss.


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