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Mountain View, CA

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reply to evanooo

Re: [hard drive] cant recover deleted files from SSD

said by evanooo :

Marked deleted != concomitant overwriting of data.

You're correct -- however, guess what SSD-oriented operation gets executed by the kernel on deletion of data (i.e. shrinking of files, deletion of files, and similar operations), under Windows Vista and newer? TRIM (i.e. ATA CDB command 0x06). And you know what TRIM does, yes? If not, here you go:


This guy basically sums it up correctly (despite the article author in comment #17 stating "I'm not so sure that's true" -- his understanding of how it works isn't right, while what the guy says in #15 is correct. "Look up table" and "virtual blocks", by the way, refers to the FTL):


So this refutes my original statement (my first reply) that there's generally no difference between and SSD and an MHDD. I'm quite happy to admit when I'm wrong, and this is one of those cases. So there you go: I was wrong.

The reason I was wrong is explainable as well: 1) I historically have not used OSes that offer TRIM capability (i.e. I use XP for my workstation, with an SSD; my servers have historically used FreeBSD which only semi-recently introduced TRIM support for UFS only), and 2) TRIM behaviour (meaning inside the SSD) actually varies based on SSD brand and firmware version. So what I've historically been familiar with (first-gen SSDs) is different than what's out there today.

However, you also have to keep in mind that just because you delete a file doesn't mean the OS itself, or one of the zillions of other services/daemons running on the system at the same time, doesn't issue a write request to the drive (for an unrelated operation). This happens regardless of drive type (SSD vs. MHDD). The NTFS journalling mechanism comes to mind, for example -- that's done under-the-hood so you wouldn't have any visibility into that happening. The last OS I used where things weren't happening in the background/"behind the scenes" was MS-DOS.

So in summary, I'm sorry for being wrong and getting you all riled up in the process. I do know a lot about storage, but SSDs (even to me) are still new and I am still learning as time goes on. MHDDs are a different story (and you can view my many posts here for justification on that).

HTH in some way.
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


its why i posted here, knew someone had to know something...because it almost never happened with non-system MHDD that i couldn't recover freshly deleted files
and its not an OS drive forgot to mention that