Mounting /home on a different device is common, shouldn't be a problem. Universities used to mount you're home dir off the network with nfs so that it followed you to any system you logged in to.

Ha, home has been traditionally always on a separate drive. That's the reason why root user has the home under /root and not /home/root, so that it can login even if the home drive didn't Mount.

As a curiosity, even /usr was traditionally on a separate drive and that's why critical binaries and libraries where under /bin and /lib while all non critical stuff under /usr. It is called "split-usr".

Nowadays /usr is always on the same drive as root, and we moved to a "merge-usr" approach where stuff under /lib and /bin is a symlink into /usr/lib and /usr/bin.

Because when HDDs where 50mb in size, even that small binary file counted as big :)

I always put /home on a different drive than /

There is no problem with having home on a different disk. But why do you want swap on the slower disk? These would benefit from being on the faster disks. Same with all the system binaries.

Personally I would put as much as possible on the faster disk and mount the slower somewhere that the speed matters less. Like for photos/videos in your home dir.

/boot can be anywhere though if you are getting a grub error that suggests the UEFI firmware is finding grubs first stage but grub is having issues after that. Personally I don't use grub anymore, systemd-boot is far simpler as it does not need to deal with legacy MBR booting.

Yes. I have an NVME as my OS drive but most of my home directory (Documents, Videos, Pictures, Music, etc.) is on an older large data HDD. My .config and anything else is still on the NVME. I use fstab to mount the directories automatically.

I believe that the only FS that absolutely need to be on the root partition are /etc and /var. The rest can be anywhere else with various degrees of tinkering. For /home to be moved, you should just need to edit your fstab (or your systemd mounts, depending on your distro).

The machine is so old that all distros play nice with it.

Lmao, I'm using X230 as my on-the-go laptop unironically. Also FYI, older machine might not work as well. RHEL based distros have started to remove the support for Sandy & Ivy in their next releases.

To answer your question, Linux doesn't care which drive you put your /home. Hell, you can even mount /var or /usr on a different drive. It only care that you list it on fstab (or mount it manually, go to town!). It would just treat them like any other filesystem.

I've never heard of that 2.5 SSD being problematic for boot drive before.

First, of course it is completely fine for /home to be on another drive. As long as it is configured in /etc/fstab correctly, almost any configuration of drives and partitions is okay.

Second, your boot issue sounds very strange. Firstly, x220 has a traditional bios boot, right? So you do not need an /EFI partition, and should install grub to the reserved space on the drive for booting (which if you configured MBR for your drive requires no change, if you configured GPT you need to reserve that space). If you have one of the x220s with libreboot (not sure if that exists, but I used to have an x200 with libreboot flashed for the bios), then your grub version might be very out of date, which could cause issues as well.