Even the lower tier IronWolf drives from Seagate specify 600k load/unload cycles (not spin down, granted, but gives an idea of the longevity).
There are many similar articles.
Or perhaps the fact that my IronWolf drives are 5400rpm rather than 7200rpm means they're still going strong after 4 years with no issues spinning down after 20 minutes.
Or maybe I'm just insanely lucky? Before I moved to my desktop machine being 100% SSD I used hard drives for close to 30 years and never had a drive go bad. I did tend to use drives for a max of 3-5 years though before upgrading for more space.
(see above, same question)
If the stuff you access often can be cashed to SSDs you rarely access it. Depending on your file system and operating system only drives that are in use can be spun up. If you have multiple drive arrays with media some of it won't be accessed as often.
In an enterprise setting it generally doesn't make sense. For a home environment disks you generally don't access the data that often. Automatic downloads and seeding change that.
If a read request can be filled by the OS cache, it will be. Then it will be filled by the ARC, if possible. Then it will be filled by the L2ARC, if it exists. Then it will be filled by the on-disk cache, if possible; finally, it will be filled by a read.
An async write will eventually be flushed to a disk write, possibly after seconds of realtime. The ack is sent after the write is complete... which may be while the drive has it in a cache but hasn't actually written it yet.
A sync write will be written to the ZIL SLOG, if it exists, while it is being written to the disk. It will be acknowledged as soon as the ZIL finishes the write. If the SLOG does not exist, the ack comes when the disk reports the write complete.
When it comes to self hosted servers for example, using tiny computers as servers often gets you massive power savings that do make a difference compared to buying off-lease rack mount servers that can idle in the hundreds of watts.
Linux ISOs?
You are thinking in dimensions normal people have no need for. Just the numbers alone speaks volumes, 12TB, 6 hdds, 8TB NVMes, 2.5GB LAN.
And these prices are getting low enough, especially with this NUC-based solutions, to actually be price competitive with the low tiers of drive & dropbox while also being something you actually own and control. Dropbox still charges $120/yr for the entry level plan of just 2TB after all. 3x WD Blue NVMEs + an N150 and you're at break-even in 3 years or less
Any idea what that failure mode could have been? It worries me tremendously to keep data on an SSD now.
Then shortly after I had a BTRFS fail without failing Hardware on another drive
Just backup your stuff with 3-2-1 strategy and you're OK.
I'd recommend a combination of syncthing, restic and ZFS (with zfs-auto-snapshot, sanoid or zrepl) and maybe bluray (as readonly medium)