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The other two drives are on the Test Machine, and the two drives function as my "NAS". They have less wear on them. They are SSDs for "fast search purposes".
The devices in the picture have a rating of "2400 TBW". You buy SSD drives like bog roll. The more TBW a drive offers, the more you pay for it. When shopping, you must do the research to find the number, as the manufacturers are <cough> "bashful".
On the daily driver, partitions occupy 25% of the device. You might ask "how are the flash cells on the other 75% used?". Well, the storage is virtualized. If you read sector 0 from the outside of the device, that could be flash sector 12345678. When sector 0 is stored, it might well be down near the end of the device. The sectors are stored all over the place. The sectors are moved inside "to even out the wear". A giant table (reliability issue???) records the mapping. The table must be correctly recorded, in the event of an emergency power fail. The firmware to do this, must be awesome :-)
This means, even though the physical partition size is 25% of the device, *all* the flash cells share the wearing action. This is how I get the "value" from the 2400 TBW. It all gets used. I'm running what's known as a "high sparing ratio", which doesn't really mean anything. I would have to manually TRIM the chunk down at the end of the drive, once in a while, so the drive knows those cells are available. I will do that... right now.
Some of the smaller relatives of those things, have "300 TBW" and "600 TBW" ratings. They're sitting in a small pile and work as scratch drives for OS installs. None of those is very worn either.
The wear estimate, takes into account write amplification, and the usage pattern of the drive, can make that better or worse. The device records the "real" usage, and the device knows how much each flash page has been used. There's a counter for each page. Via wear leveling, at end of life, the counter would read "599, 599, 600, 601, ..." indicating the wear leveling algorithm works very well indeed at sucking the maximum life out of the cells. Unlike in a USB flash stick where it reads out "600, 0, 0, 0" indicating uneven wear and "a hole was burned in the TLC". SSD wear leveling is what makes champs of them. Based on the failures I'm getting on USB TLC based flash sticks, my conclusion is they "suck on leveling". SSD drives are very much better than USB flash sticks.
*******One drive, intended for Chia coin mining, has "12000 TBW", and the price was not disclosed. People might well have been buying those from the manufacturer directly. Like a thousand a piece or more. Those see the worst possible write behavior (imagine beating the piss out of a disposable hardware costing a thousand). That's why they need the 12000 number. A hard drive could exceed the 12000 number, but... the storage would be "slug slow" by comparison.
So capacity is one thing. Obviously, you buy capacity to store your goods. If you have 1TB of goods, then you need at least a 1TB drive. But excess capacity is not lost, as like a "bog roll", you get to use the entire roll.
Now, one of those could just "up and die" in the next ten seconds. I cannot predict what that statistic is. First generation devices had terrible firmware. When Intel got into the business of making SSDs, they nearly had a "s*it-fit" when then examined the source for that firmware. There was a marked improvement in industry practice, and I have no idea what went on behind the scenes. There are still occasionally bad firmwares (like the Samsung 2TB NVMe issue), but for the most part, they're every bit as predictable as HDD. Seagate has botched HDD firmwares too. Sometimes you have to flash up a HDD, before it is too late (metadata corruption).
Be aware, that people buy HDD, they clone over from old HDD, they erase the source HDD, and a couple days later... the new HDD dies. To avoid issues with infant mortality when cloning over, you should wait a couple months to see if the new drive is a champ or not.
If you hear a new HDD "clicking", that is generally a bad thing. I discovered a brand new HDD drive here clicking, and it turned out the root cause was the power supply was running at 11.6VDC . The drive is supposed to accept +/-10%, but it was obvious the voltage detector on the drive was using a much tighter window than that. Some HDD will get into a "spin down/spin up" loop due to the voltage issue. So when you hear a drive click, use your multimeter and verify that +5V rail and +12V rail are not too far out of spec. Now, that new drive, does not have to go back to the store.
The new supply is running at 12.27 VDC. If the power supply voltage rose to +15V, then a protection device on the drive will start to burn, and the drive will stink :-) Because the controller board is upside-down, you can't even see the black spot. The protection device exists to clobber HotPlug transients, and is not intended to "discipline" hard drives for going out of spec.
Paul