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Data Recovery From an External Hard Drive

A Primer on Hard-Drive Data Storage

The data storage methods for hard drives, external or internal, are actually fairly simple to understand. What is not easy is to understand the process of data recovery from an external hard drive. As new data is written to the hard drive, “free” space is overwritten on the drive in a series of fragments. Usually the hard drive will try to write all these fragments next to each other in sequence, but this isn’t always possible and this is why defragmentation is sometimes required. The location and sequence of fragments is stored in an a separate sector, so the hard drive knows how to find the files spread across it’s storage. When a file is deleted, this separate storage is overwritten and so the hard drive believes the space to be free.

Source: http://www.freedigitalphotos.net

How Does This Connect to Lost Data?

The most common and simplest way to “lose” data from an external hard drive is simply to accidentally delete it. When this happens, the hard drive “forgets” where it stored the old file but it does not erase the data stored on the disk itself. Only overwriting old data will truly erase it. Thus, whenever a file is lost to accidental deletion, the best thing to do is immediately shut down the computer and disconnect the hard drive to prevent new files from overwriting the old. There is a large volume of software that can scan the so-called “free” space on a hard disk to detect files that have been forgotten by the hard drive. Many of these software can be made into a bootable CD or flash drive to further protect your files from new write operations.

What About Other Types of Lost Data?

The other ways of losing data are a little more difficult to fix. Hard drive corruption can happen in any number of ways. A power surge, scratches on the read surface, or a particularly harsh drop can all cause damage to the physical disk and thus corrupt files. These are the hardest files to recover, because the information has, for all intents and purposes, been physically destroyed. Sometimes the damage is only to insignificant fragments of otherwise important files. When this is true, the important parts of the files can be recovered and the data “healed” to produce a readable file that lacks the physically damaged fragments. Many companies specialize in exactly this, and a few pieces of software exist that claim to be able to repair the damage. In general, it is better to use a recovery service than software, as the software is typically without guarantee and uses less precise methods.

What if The Hard Drive Dies?

This is the absolute worst case scenario. The same factors that lead to physical damage can lead to complete hard drive failure. In this case, there is nothing software can do to help, and only very specialized equipment can be used to extract data from the disk. Often times this will lead to a complete disk recovery, as many hard drive failures are not directly tied to the read area of the disk, but this is by no means guaranteed. Depending on the scope of the damage, it may or may not be possible to recover any data from the disk. The process is also very labor intensive, so it comes at a significant price. Still, hard drive failures will happen even if precautions are taken against it, and when that failure causes the loss of a significant number of critical data files, it can be worth the cost.

About the author

Praveen Rajarao

Praveen Rajarao is an Entrepreneur and in his spare time blogs on his website –http://www.dailymorningcoffee.com and http://www.pbgeeks.com. His topics range from blogging to technology to affiliate programs and making money online and how-to guides. Daily Morning Coffee is also accepting Guest Posts from Professional Bloggers at this time, take a look at “Write For DMC” page for more details on the same.


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  • I’ve had a hard drive crash and it needed to be recovered. I was told it would need to be sent to a clean room, because they needed to physically open it up.

    I still have the drive, in the hope that one day I can afford to recover the lost photos.

    Until then, I’ve got a raid system and back-up frequently. It is helpful to understand how they work, though, and that is why I liked the post. Good job.
    Brian D. Meeks ( recently posted…A Call to ReadersMy Profile

  • Thanks for the explanation, Praveen 🙂

    Is it the same for internal harddrive? (How do you recover data for a Windows – let’s say vista – that has been “permanently” deleted?

    Does Shift+Dlt truly erase the data? Or can we recover it?

    I have heard of Macs being able to recover the data that has been deleted (apart from using Windows restore, is there any other way to recover permanently deleted data?)

    • Jeevan – I am sure everyone will have these questions when it comes to recovering data. In a home environment, with just one personal laptop or PC, a permanently deleted file or data is gone for ever.

      However, when it comes to an enterprise, you can expect your network team to recover the data in case it was deleted from a server.

      Hope that answers your question, but yes it got me thinking too 🙂
      Praveen Rajarao recently posted…Make a Positive Difference on a Volunteer Placement AbroadMy Profile

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