Wipe Free Space/MFT on SSDs

[LuvenRN]

Most excellent folks at Piriform,

 

I'm a long time user and sheepishly admit to only now having finally gotten around to "contributing" via PayPal. Go have a pint or two on me then get back to work on your excellent products!

 

I was recently watching my computer stats as CCleaner went through it's "wipe free space" and "wipe MFT" process. Based on the comparatively slow rate at which free space is consumed, it appears to me that CCleaner is grabbing bits of disk space then wiping it and moving on to the next until all free space is "owned." The space is then released and MFT wipe started.

 

I'm concerned that the current wipe approach may not be effective using Solid-State-Drives (SSDs) such as I use in my computer. This because a write to a new sector may, in fact, cause the Flash Controller in the SSD to simply remap a fresh sector to the new write request. Thus, the old sector would remain in the "free list" of sectors in the SSD Flash Controller.

 

If I am correct, the actual sectors wiped would vary depending on how the SSD Flash Controller allocates sectors. If it always allocated from the head of the list, then the current wipe process would eventually get them all. Unfortunately, I believe most Flash Controllers use a more sophisticated allocation scheme involving least-written determination. If this is true, then the actual sectors written would be unique to any individual SSD and very hard to predict.

 

It would seem a better way to perform wipe on SSDs would be to grab up all the free space so there is no "free list" of unused sectors then perform the wipe of free space and the MFT. Since most SSDs maintain some "spare" sectors, there may need to be some additional thinking put into this.

 

I'm no expert in these matters, and I could certainly be wrong. If I am correct, then my concerns would apply to Compact Flash cards, thumb drives, and so forth as well as SSDs.

 

Bottom Line: Does CCleaner reliably wipe SSDs and other devices with sector remapping performed by a Flash Controller?

 

Thanks for the great products and your attention to this post!

[JDPower]

I was recently watching my computer stats as CCleaner went through it's "wipe free space" and "wipe MFT" process. Based on the comparatively slow rate at which free space is consumed, it appears to me that CCleaner is grabbing bits of disk space then wiping it and moving on to the next until all free space is "owned."

AFAIA CCleaner basically fills the entire free space with a large empty temp file then overwrites it in one go.

[LuvenRN]

AFAIA CCleaner basically fills the entire free space with a large empty temp file then overwrites it in one go.

 

If it were doing that, then I would expect to see all my free space disappear quite rapidly then see a long delay while it wipes the file. In fact, what I see is that the empty space is consumed slowly, and CCleaner declares free space is wiped as soon as the free space has been consumed

[Augeas]

There's never been any published details about how CC works, not that I've seen anyway. I would say that CC writes 4k (or whatever) blocks of zeroes as it goes along its merry way until all the free space is consumed. I don't know whether CC overwrites the MFT in the same way as other wipers or not. I get the impression that CC, by it's relatively small size, is not as sophisticated a free-space wiper as a specialist program such as Eraser.

 

I don't know much about SSDs. A hd wouldn't write blocks sequentially, but in a first available space pattern. But as the entire disk is being filled then the order of writes doesn't really matter.

 

There have been concerns raised elsewhere about the suitability of wiping free space on SSDs. You'd have to search Google for this.

[Andavari]

I get the impression that CC, by it's relatively small size, is not as sophisticated a free-space wiper as a specialist program such as Eraser.

There aren't many other freeware, open source, or even commercial wipers, that can even compare to how successfully Eraser wipes the free space which is a tell tell sign when rivals are done so fast with it - while Eraser on the other hand spends much more time.