this post was submitted on 03 Sep 2023
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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Excellent question, and for people who have SSDs it's worth knowing the answer.
Very simply, SSDs store data differently than HDDs, and when a file is removed, sectors on SSDs have to be explicitly cleared instead of simply waiting to be overwritten like on HDDs. Not doing so on a regular basis decreases the lifespan of the SSD. Crucial (a SSD manufacturer) explains it here much better than I can:
https://www.crucial.com/articles/about-ssd/what-is-trim
I have never read much about trim before. Now I'm curious about something: if an ssd was trimmed, is all deleted data lost? Is filling an ssd with random data unnecessary if we want so safely delete something?
What exactly happens when you issue a TRIM depends on the SSD and how much contiguous data was trimmed. Some drives guarantee TRIM-to-zero, but there's still no guarantee that the data is actually erased (it could just marked as inaccessible to be erased later). In general you should think of it more as a hint to the drive that these bytes are no longer needed, and that the drive firmware can do whatever it likes with that information to improve its wear-levelling ability.
Filling an SSD with random data isn't even guaranteed to securely erase everything, as most SSDs are overprovisioned (they have more flash cells than the drive's reported capacity, used for wear leveling and the likes). even if you overwrite the whole drive with random bytes, there's a pretty good chance that a number of sectors won't be overwritten, and the random bytes would end up going to a previously unused sector.
Nowadays, if you want to wipe a drive (be it solid state or spinning rust), you should probably be using secure erase - it's likely to be much faster than simply overwriting everything, and it's actually guaranteed to make all the data irrecoverable.
Thank you for your response, I didn't know about secure erase. Looks like my knowledge is a bit outdated.