Since I usually only visit the forum to ask for help, I figured I'd also share something useful for a change. Hopefully that still makes this the right forum section, feel free to move if not.

For some time I've been facing a dilemma: Hard Disk Drives are very slow, but more reliable as well as cheap when it comes to price per TB of storage. Solid State Drives are very fast, but you need to make sure you aren't writing too much data to them while leaving enough free space to give it plenty of free cells to cycle between as to further reduce wear. Like most people, I was previously using a two drive setup, with an SSD for the root partition and an HDD for the home partition. The issue with this is that while boot times are very fast, logins are not, and the general user experience is often painfully slow when working with user data. Of course relying on an SSD to store all the data in your home folder is more risky, plus a 2TB SSD costs as much as an 8TB HDD so it's too expensive for most of us.

I found a way to get the same unified experience under an optimized 3-drive setup; A NVME (PCIE) SSD for the root partition, a SATA3 SSD for the home partition, and a SATA3 HDD as an archive partition. It works like this: /archive/myusername follows the same structure as /home/myusername except it contains only large directories with stuff I wish to ensure I don't risk losing and / or is updated more heavily (media, GIT repositories of projects compiled from Github / Gitlab, etc). /home/myusername meanwhile contains all the user settings and stuff the system needs to work with, such as the ~/.config and ~/.local and ~/.cache directories with everything else of the sort. For further reliability I use a rsync command scheduled with cron, to backup some of these settings directories from the SSD to the HDD on a daily basis... in case the home SSD ever crashes I can easily recover them too from the archive HDD. Finally I use symlinks to seamlessly connect everything from my /archive directory to my /home directory, making it possible to access all data as if in the same place; Directories such as My Pictures / My Videos / My Music and more are located on the HDD but linked to the SSD so they appear part of my home directory as usual. Here's a screenshot of exactly what this setup looks like:

https://i.imgur.com/vMiQw6H.png

The practical differences I instantly noticed after the drive change: Apart from gaining a bit of extra free space on the old HDD by splitting some data that's not being duplicated, logins are now lightning fast like boot times and so is opening applications! The performance is in fact faster on the hard drive as well, thanks to it not being automatically accessed by applications constantly reading or updating their settings, but only used when I'm deliberately accessing it to look at something... less cases of processes freezing due to going into "disk sleep" too. Since the hard drive is nearly 10 years old I'm protecting it from added stress, both drives share the load and should thus last longer. On my home SSD I'm using roughly 10% of the 1TB available, while writing is mainly limited to updating small settings (eg: Firefox browser cache) which should ensure little overall wear. I sense no difference from my previous setup thanks to the symlinks, everything looks and feels exactly the same way except for the little arrow on the icons.

I figured this would be inspiring as I imagine many people going for such a setup. To me it seems like the ideal configuration at this point in computer history: A small NVME SSD for installing the OS / EFI partition (500 GB or less), a larger SATA3 SSD for lightweight home data (1 or 2 TB), then an even larger SATA3 HDD for storing heavy data you don't mind being accessed slowly (4 TB or more)... I found this the most efficient and affordable way to get the best of both worlds at the moment. Hope others find this suggestion helpful! What are your own thoughts, and can you think of ways to better improve this kind of integrated drive configuration?

"To me it seems like the ideal configuration"

I think that says it all as far as your choices.

Guess things like raid/lvm/zfs could make difference and even how you manage swap.

Personally, I just run a ssd like a mechanical usually. By the time it fails, there were be a new shiny faster, bigger and better one I'll buy. I have one home system that has almost everything on ssd except the media which is on an enterprise mechanical drive. It cost almost the same as ssd but hope to recover it MTBF.

I run only SSD and don't worry about failure because I back up to my NAS. I have been using these SSDs (one for OS, one for /home) for 4 years and their wear is minimal. Buy a quality SSD and don't worry about it. Just back up your data like normal.

Glad you found a setup that works for you.

I have pretty much established that I am just keeping the basic "at the moment" stuff I need on my laptop which has an SSD, and that any more long term or older stuff is getting backed up to my server which has a regular hard drive in it.

I backup to an external USB drive too. Still worried about losing any of my home directory data though... so with such a setup it can be optimized easily, to have the lightweight and less-important stuff on the SSD where it can be read quickly while also backing up the more important parts back to the internal HDD.

Better setups for other use cases exist too of course. I never used RAID since it always gave me this feeling that it's tangling multiple drives together in bizarre ways, I prefer sticking with AHCI. If both drives are designed to work together and have the same size though, that could work better for other configurations.

I wholeheartedly agree with the ssd + hdd scenario.
I add an additional quirk in that the hdd portion of my /home is actually raid5 so it can handle a single drive failure without data loss. That is also backed up daily to an NAS.

Speed is important. Reliability is just as important (or more so) and raid5 with backups gives me that. Raid0 or 1 is overall less reliable than raid5.