wrote:
I have a 10 year old Dell that came with an approx 960 GB HDD.
3 years ago I added an approx 240 GB SSD to serve as C: and D: ,
and elevated the HDD as F: for large items, photos, music, etc.
Both the HDD and SSD have always performed flawlessly, but was
wondering how long I can expect this to continue. Thoughts ? ...

SSD has Toolbox software, and will tell you "Percent Life".
This is 3000 writes times 240GB. Once you've done that
much writing, the Life is "0%". The Toolbox is responsible
for predicting remaining life, and it can do this by
checking the stats once a day and "projecting" end of life.

On the HDD, you read out the SMART and check

Power On Hours - I have one at 55000 hours

Reallocated Sectors, Data Column 0 - indicates threshold hasn't been
reached yet for reallocations. Mine
might span 0..5500 as value range.
Approaching 5500 is "zero life remaining"

You divide the 55000 hours by 8 hours per day, then
figure out how many years that is, as an estimate. I've
had drives spinning (no power save modes) for seven years
continuous, but they were getting pretty cranky at that point,
and that drive didn't even use FDB (fluid dynamic bearings).
That was a ball bearing motor.

The FDB motors in hard drives could last forever,
as the motor is "zero friction". But real motors,
the lubricant leaves then, and the motor then seizes.

Modern drives probably die of head crashes, as the
flying height is very very low. They have excellent
shock ratings, but some of the statistics for hard
drives, suggest a "wear pattern", as if somehow
the head is contacting the surface or something.
There aren't a lot of post-mortem carried out on
hard drives, to know the exact failure mechanism.

It's possible a Helium filled drive could last
longer, but the Helium is only guaranteed to be there
for about five years, and the seals are not perfect.
After five years, it's anyones guess when they'll
have a Helium failure.

Your drive is not Helium filled and has a breather
hole. A 14TB drive might have Helium in it. The
Helium drive lid is held on with an adhesive.
That holds the gas.

HTH,
Paul