This is another question that gets my most common answers: “maybe” and “it depends”.
It might be possible to recover old data from an external hard drive — or any hard drive — as long as a few conditions are met.
I’ll review what those are, and then I’ll recover some files from an external drive I recently formatted.
Become a Patron of Ask Leo! and go ad-free!
The conditions for success
There are several things that conspire for or against successful data recovery. The more of these conditions that are met, the higher the chances you’ll be able to recover old files.
If you formatted, you used quick format
I suspect that accidentally formatting the wrong disk is one of the more common reasons folks need data recovery success. The good news here is that as long as you didn’t specify “full” format — in other words, you opted for a “quick” format — you dodged a large bullet. A full format overwrites the entire hard drive, rendering its contents inaccessible to mere mortals.
You’ve not used the drive since deleting anything
Recovering data is easier on an external drive than an internal one. If you delete a file from an internal drive that contains the operating system, the data can be unrecoverable because the hard drive continues working, potentially overwriting the file. If you mistakenly delete a file on an external drive and stop using the drive completely, your chances of recovering it are good, regardless of how much time has passed.
You’ve not used the drive for “much” since deleting
Now we start getting into grey areas. The more you write data to a drive, the lower your chances are to recover what was there before. If you delete a bunch of things and then use the drive, causing a small amount of data to be written to it, chances are better than if you cause a lot of data to be written. How much “a little” or “a lot” is undefined.
You’re looking for something small
If they can be recovered at all, small files are more likely to be completely recovered than large files. The larger the file, the higher the chances that intervening use will have overwritten portions thereof.
You get lucky on layout
Depending on exactly how the drive was used before the file you’re looking for was created, when it was created, and after it was deleted, you could get lucky. In concept1, if there’s a lot of data on the drive when the file was created, and if much of that pre-existing data was deleted before the desired file was deleted, it’s possible that what you want is on a rarely-reached portion of the hard drive, and therefore more likely to be recoverable.
You just get lucky
There’s just no getting around the fact that if the drive’s been used for anything that involved writing, previously deleted data is at risk. A good portion of successful data recovery boils down to sheer luck on where the desired file happened to be written on the disk, and whether any of it has been overwritten in the time since it was deleted.
Recovering data from an external hard drive
A few days ago, I formatted an old 500GB external drive that I hadn’t used in a long time. I fired up Recuva and had it scan the drive. Its quick scan turned up nothing, but it offered a “deep” scan, warning it might take some time.
“Deep scan” results began to show almost immediately.
True to its word, five hours later, it had completed.
Apparently, I had stored music on this drive at some distant point in the past. While Recuva was able to list the files, and claimed over 109,000 files were found, my attempts to actually recover files were unsuccessful. The files recovered were not the actual, original files, and could not be played.
This goes to show that when it comes to file recovery, time is of the essence, as is lack of activity. This might be my oldest external drive3, and it was used heavily. Clearly, all that use invalidated the information on the drive, preventing successful recovery of its prior contents.
Try your luck
It is possible to recover information from old hard drives, but so much depends on exactly what was done with the drive since the original data was removed that it’s nearly impossible to say with any certainty what will be there.
As soon as you realize that you may need to recover deleted data from any drive, stop using the drive.
Then give tools like Recuva a try.
If you found this article helpful, I'm sure you'll also love Confident Computing! My weekly email newsletter is full of articles that help you solve problems, stay safe, and give you more confidence with technology. Subscribe now and I'll see you there soon,
Footnotes & References
1: In concept. Various disk formats have differing strategies on where to place data on hard drives so as to minimize wear, so it’s possible that this might not even apply. But you could get lucky.
3: It’s actually a “limited edition” Seagate FreeAgent Go, engraved with the old Ask Leo! logo.