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Headphoneus Supremus
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You're getting this completely wrong. The stuff they use in flash drives and SSDs are completely different. There's a reason we see servers using SSDs and not flash drives for storage.
The tech used for flash drive NAND chips is eMMC which is cheap to make and poor performance. Solid state drives use a much more different kind of NAND, which is why we don't see our flash drives with NAND capable of doing 700-900MB/s of read/write like most SSDs do nowadays (ignoring interface limitations).
And here's the TLC lifespan article if you want some numbers for the shortest living type of NAND we can find in consumer SSDs right now: http://www.anandtech.com/show/6459/samsung-ssd-840-testing-the-endurance-of-tlc-nand
Keep in mind that lifespan depends on the amount of NAND chips you have as well since wear is spread over all of the chips. Even with a 128GiB TLC SSD you're looking at 11.7 years at 10GiB of read/write per day. That doubles with 256GiB drives and etc.
There is no reason to just keep the OS on disk. You're wasting free space and time (since it loads up programs waaaay way faster) by just having OS on there. You only get a boot speed boost and that's it. Everything from there on out is slow if it's not regarding the OS.
I don't know where you thought SSDs use eMMC like flash drives but that is completely wrong. There are countless servers that use ONLY SSDs as their storage medium and they write hundreds to thousands of gigabytes per day (if not even more). If they used eMMC, sure they'd be dead in a few days but there's a reason these servers can use SSDs.
Thanks for the clarification.
When I first googled what SSD is and what is it made of, someone write that it is made of the same thing as USB flash drives, and they will eventually reach out of data.
I was curious about TRIM, or what they use to not re-write the same cells. Is this feature embedded in the firmware of the SSD, or the OS should do this?
TRIM is OS side, Garbage Collection is built into the SSD.
I'll explain quickly why we have these 2 things for SSDs but not HDDs along with the differences between them. HDD's can rewrite over old data without any issues.
NAND chips, however, cannot do this; You have to erase the old data before you can write in new data. Our operating systems don't have a built in mechanism to do this because they're adapted to HDDs; they only mark the space as empty but the data is still there and, since NAND chips cannot write onto places with existing data, you end up with this dud space that's marked as empty but cannot be written to.
So in order to further explain GC and TRIM you need to know the structure of SSDs (most modern storage devices use this structure actually). Everything is broken into different layers of organization. The first layer is the hardware layer, aka "blocks." On SSDs, however, blocks are broken up into "pages" which are made up of some individual NAND cells. Pages are the smallest units SSDs can write to (they're usually 8KB acording to ArsTechnica).
Operating systems can't see the physical structures of our drives; they only see some total volume and some other stuff. Operating systems use file systems that adds another organizational layer on top of the physical structure discs have and it sets its own cluster size and way of distributing files. You start to see the disconnect between OS and HDD/SSD: the OS only sees the file system, so it's up to the SSD controller to know how to write the data to the NAND chips.
So SSD fundamentals: SSDs can read and write at the page level but for some reason they cannot ERASE at the page level. They can only erase entire blocks since the high voltage they apply will end up also wiping or altering all the other pages within the block.
So in order to get around this, SSD controllers have a built in routine called garbage collection. The OS only marks pages as stale/empty and the controller can see that. What garbage collection does is it looks in every block for all the good and stale pages, then copies all of the good pages to an empty block, then wipes everything in that old block and marks it ready to use. It gets weird though since when a file system has something marked as "deleted" it can still look like a good page in some occasions and ends up being copied by GC.
This is where the TRIM command comes in (it's not an acronym. Technically it's just Trim). TRIM is the bridge between the file system and blocks that helps SSDs mark pages as stale when the contents of those pages are deleted so garbage collection can do its job properly, aka not copying stale pages over that should have been deleted. Note that TRIM is not a replacement for GC, they work together.
TRIM isn't that necessary anymore since GC algorithms have gotten good enough to not need it but it makes the process more efficient and helps avoid GC marking stale pages as good.
Sources: http://arstechnica.com/gadgets/2015/04/ask-ars-my-ssd-does-garbage-collection-so-i-dont-need-trim-right/
http://www.thessdreview.com/daily-news/latest-buzz/garbage-collection-and-trim-in-ssds-explained-an-ssd-primer/