If you need 4TB of fast storage why not just RAID some good 1TB drives? Will be heaps cheaper and likely as fast as you'll need
As for small capacity SSD's, I'd be careful what you buy under 500GB. SSD's (especially mid and lower grade) have a finite lifespan of reliable writes. The more you overwrite and pack a drive full, the faster it will fail. I killed a 128GB SSD in less than a year from constantly dumping files on and off of it.
Their life span does seem a little shorter but at the same time, everything is being made cheaper and more disposable. And when it comes to laptops, SSD's are lasting longer because spinners dont like being moved/any impact, especially when they are powered up.
The lifespan of an SSD comes down to its technology. If it doesn't have a good onboard controller and very little or no cache, it can constantly re-write certain sectors corrupting small areas of the SSD and degrading performance and stability. Obviously that's less of an issue the larger the drive. Mechanical drives are just that, mechanical, they fail.
I dunno man ive never had a spinner fail on me. The ol family computer ran over a decade. I have also only had one SSD fail and it wasnt a critical failure it was just generally running like shit.
I've got some ancient harddrives too, but they have bearings, and they dry out and the drive will fail. I believe running a mechanical drive 24/7 helps increase life, I've known of a LOT of mechanical drives that work for decades, operating daily, but as soon as they are left to sit 2-3 years and booted back up, thats when bearing and arm failure show up.
since installing my SSD I can now play many large large games , thanks to this thread giving me the 'push' I've grown to love that shitty SSD cheers