I replaced my laptop's DVD drive with a HDD caddy adapter, so it supports two drives instead of just one. Then, I installed a 120G SSD alongside with a 500G HDD, with the HDD being connected through the caddy adapter. The entire Linux installation on this laptop was done in 2019 and, since then, I never reinstalled nor replaced the drives.

But sometimes I hear what seems to be a "coil whine" (a short high pitched sound) coming from where the SSD is, so I guess that its end is near. I have another SSD (240G) I bought a few years ago, waiting to be installed but I'm waiting to get another HDD (1TB or 2TB) in order to make another installation, because the HDD was reused from another laptop I had (therefore, it's really old by now, although I had no I/O errors nor "coil whinings" yet).

Back when I installed the current Linux, I mistakenly placed /var and /home (and consequently, /home/me/.cache and /home/me/.config, both folders of which have high write rates because I use KDE Plasma) on the SSD. As the years passed by, I realized it was a mistake but I never had the courage to relocate things, so I did some "creative solutions" ("gambiarra") such as creating a symlinked folder for .cache and .config, pointing them to another folder within the HDD.

As for backup, while I have three old spare HDDs holding the same old data (so it's a redundant backup), there are so many (hundreds of GBs) new things I both produced and downloaded that I'd need lots of room to better organize all the files, finding out what is not needed anymore and renewing my backups. That's why I was looking for either 1TB or 2TB HDDs, as brand-new as possible (also, I'm intending to tinker more with things such as data science after a fresh new installation of Linux). It's not a thing that I'm really in a hurry to do, though.

Edit: and those old spare HDDs are 3.5" so they wouldn't fit the laptop.