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How Often Should I Wipe Hard Drive Free Space?

Does never work for you?

Free space wiping removes the ability to undelete files. Whether or not you need it, or how often, depends on how interesting your data might be.
A surreal scene showing a standing maintenance person using a floor polisher on a giant hard disk platter. The maintenance worker, dressed in a standard blue jumpsuit and safety shoes, is actively operating the large, mechanical floor polisher.
(Image: DALL-E 3)
Question: I read your article about CCleaner’s file deletion overwrite, which I tried. Mine took about three hours to do. My question is how often should I use this file deletion in general? Once per month? I am really clueless about that. I am referring to the CCleaner’s wipe section.

Well, let me put it this way…. never is what works for me. I never run it.

With that having been said, let’s look at why you might want to run it, and from that, see if we can come up with some ideas for how often it might make sense to run.

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Wiping hard drive free space

Free space wiping with tools like CCleaner’s Drive Wiper prevents the recovery of deleted files by overwriting them. While helpful for sensitive data, for most, the risk is minimal, and regular wiping is really unnecessary. If you do store sensitive data, then exactly how often depends on the situation, and the data.

Deleted files aren’t deleted

By now, I think you probably realize when you delete a file — even emptying the Recycle Bin, if that was used — the data that was contained in the file remains on the disk. The area that contains the data is marked as free, but the data is not actually overwritten until a new file is written in exactly the same place sometime later.

And later could be milliseconds or it could be months.

Thus, until that overwrite actually happens, we have the ability to “un-delete” a file using tools like Recuva.

Drive wiping utilities

CCleaner's Drive Wiper
CCleaner’s Drive Wiper (Image:

CCleaner’s Drive Wiper is one example of a tool that is meant to remove this ability to undelete.

The concept is simple. The drive wiper just writes data of some sort in all of the spaces on your hard disk where no files are currently stored: all the space that’s marked as free. As a result, anything left in that free space that could have been used to recover or un-delete a file is removed.

If you have a lot of free space, that could take some time.

How often?

Now, to your real question: how often should you do this?

As with so many things, it depends.

To me, it depends on three things:

  • It depends on how sensitive the possibly recoverable data might be.
  • It depends on how likely it is your hard disk is to fall into the hands of someone else.
  • It depends on how likely it is someone who ends up with your hard disk will bother to see what’s in the free space.

It’s that last one that, for me, reduces the need for free space wiping to near zero for most people.

I’ve said it before, and I’ll say it again: we’re just not that interesting. Smile

And, perhaps more to the point, there’s probably much more interesting stuff than deleted files. If a thief wants to go spelunking for data, they’ll probably find plenty in the files and folders that haven’t yet been deleted.

Sometimes they are after you

On the other hand, perhaps you are the target of someone’s attention. Perhaps you do have a sensitive job or work in a sensitive industry where data theft and espionage are not only possible, but even likely.

There are several additional steps (like encryption) that you should be taking, but when it comes to free-space wiping, then I’d be doing it often.

If it’s important, I’d do it nightly.

But, as I said, it’s just not that important for the vast majority of people.

Sometimes, they’re really, REALLY after you

Everything that I’ve discussed above applies to what CCleaner terms a “Simple Overwrite (1 pass)”. A simple overwrite does exactly what’s described above: it overwrites the free space and prevents common file recovery utilities from undeleting deleted files.

If someone is seriously after your data, that could potentially be not enough.

As I discussed in What difference does multiple-overwrite delete really make? there are techniques — expensive techniques — that can be used by those who are sufficiently
motivated to recover some or all of the data that has been overwritten once.

The solution is to overwrite it more than once. CCleaner offers the option of overwriting 3, 7, and even 35 times. Important: this applies only to traditional magnetic hard disks. Overwriting SSDs once is all you need.1

Do this

For most folks, doing it zero times is plenty. More important, perhaps, is erasing the hard drive completely before you give it away. But while the machine is in your possession, it’s just not something that’s worth it.

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Footnotes & References

1: There are conflicting opinions as to whether the SSD “Trim” command, run when you “optimize” the drive, is sufficient.

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