again, how long, and how long are the different life expectancies of a 512gb drive vs a 1tb? in the real world, does it in fact matter? (am asking...).
I answered that partly above, in short the difference will be measured in years. You can use up an entire SSDs life expectancy by writing to it excessively in a matter of 3-5 years if you really try. For anyone else you should expect at least twice that, 6-10 years. Many users won't write much data onto their SSDs and will see a lifespan beyond 10 years where it's then a question of what other component might fail first.
To be more precise, there isn't a general rule of thumb for 500GB vs 1TB SSDs. With a 500GB SSD for example you can spread out the data onto four 128GB NAND flash memory chips or two 256GB ones. Overall the 4x128 version could have a slightly higher endurance since the writes can be spread across more chips, though it won't necessarily double the endurance since the chips themselves have a lower capacity and thus a lower individual endurance rating.
There are a few things we know though:
- The current M2 Macs with only 250GB of storage use a single chip and all other bigger Apple SSDs use at least two chips. So these tiny M2 Apple SSDs will have very roughly only half the endurance of 500GB+ Apple SSDs. We can also see that the performance is roughly cut in half as well due to this. Conclusion is to avoid 120GB and 250GB SSDs if you want a high endurance rating and best performance.
- Often SSDs with 1TB of total capacity have about twice the endurance of 500GB SSDs.
- Usually the endurance does not increase beyond 1TB, so 2TB SSDs won't be a better buy unless you need the extra capacity.
So 1TB and up SSDs will nearly always give you the best endurance rating for the money. At least with Apple's SSDs it's easy to say that, with other manufacturers there are literally hundreds of different SSD models out there that use higher or lower quality NAND flash storage chips and you can't determine the endurance purely based on capacity.
How much can you write to an Apple SSD, what are the actual numbers? As I wrote above:
For reference, the M1 Macs are known to have flash storage that can be overwritten roughly 2.500 times before actual failure occurs. For a 500GB Apple SSD you can expect to write a full Petabyte, and once it reaches 1.25PB you can expect the SSD to be dead.
For example my own 14" Macbook has seen heavy workloads for a full year but has 64GiB of RAM, so swap space is rarely used. The SSD reports 7TB written in total and more than 99% endurance remaining. Based on this usage the SSD would easily last 20 years and more (ignoring aging components). If I only had a tiny SSD with a much worse endurance rating, it would still last well above 10 years.
To put this differently: Calculating 7TB/1,25PB comes out to 0,56% of life expectancy used up (as in the quote above) within one year.
And if I had a tiny SSD with a worse endurance rating, let's say half of that, I'd have used up 1,12% in one year. Let's say I use this Mac for 6 years, which sounds fair to me, 6,72% used up (again, if this was a worse rated SSD than it actually is). Now how much data would I have to write to this SSD every year to kill it in the 6th year? I'd have to write 104TB to it every year, to kill a 250GB M2 Apple SSD once 6 years are up.
That's actually not a great endurance rating if that were true - which it might not be, I just assumed some low fantasy endurance rating for a 250GB M2 Apple SSD. But even then, writing 104TB per year to a 250GB SSD just via swap space usage should really be impossible, in my opinion. And what write heavy applications could you let loose on such a tiny SSD in the first place.
/Edit: But I do not mean to imply that it is ok for Apple to downgrade the 250GB SSDs in their newer M2 Macs to cut endurance and performance in half. That is really really bad behaviour to make the successor much slower, and not even mentioning it anywhere.