Best way to combine SSD and HDD in iMac 2012

[MarkEJohnson66]

I've got an older (late 2012) 21.5" iMac running MacOS Catalina (10.15.7). Several years ago it was too sluggish for me, and I figured the problem was its original 1 TB HDD. However, this iMac model is difficult to upgrade internally, having a glued glass monitor panel and other tricky aspects to disassembly. Instead I bought an external SDD (also 1 TB) and just connected it via USB 3. Then I made that my boot volume. Even via the external USB interface, it worked great! It breathed new life into this old machine.

Now it's a few years later, and that SDD is just about filled. I think that's why this iMac is slowing down again. However, I'm not using the original HDD at all. I transferred ALL of my data over to the external SSD: the operating system, applications, data/files/photos...everything. I believe I can squeeze a couple more good years out of this iMac by intelligently offloading a bunch of that data back to the HDD.

I read about Fusion drives, but it sounds as though that isn't supported for EXTERNAL SSDs. At least, it's really, really not recommended. That's too bad, because it sounds like a slick solution. But not the only one, right? What's the sensible way for me to offload much of what's on the SSD back to the (unused) HDD and use both drives seamlessly?

Thanks

 

[DeltaMac]

I suggest that if you try that, and use the internal hard drive, you will be reminded of the reason that you chose to use the SSD in the first place -- that internal hard drive is a 5400 rpm laptop drive, and will still be slow!
I have upgraded several 2012 to 2014 iMacs, replacing the hard drive with SSDs, and also upgrading the RAM memory (which added to replacing hard with SSD, I think makes the repair worthwhile).
Yes, opening up that iMac is challenging, but there's good guides to follow (iFixit.com has a good repair guide for that), and I always use the admonition "Set aside a lot of time for this, Don't be in a hurry. Delicate stuff in there, particularly if this is your first time inside, so, take your time. (Buy the re-taping kit before you start)"

 

[Macky-Mac]

Just get another external SSD to use in addition to the one that's your boot drive, and just forget about the internal HDD. As DeltaMac suggests, you wouldn't be happy using the old HDD anyway.

How much free space you have on the current SSD?

 

[MarkEJohnson66]

Just get another external SSD to use in addition to the one that's your boot drive, and just forget about the internal HDD. As DeltaMac suggests, you wouldn't be happy using the old HDD anyway.

How much free space you have on the current SSD?

Yeah, good point. I could even get an external 2 TB SSD for not too much. My current 1 TB external SSD has about 115 GB free.

 

[Fishrrman]

Don't stop using the external SSD as a boot drive.

If it was getting full, it was a good idea to move SOME of the stuff on it to the internal HDD.

But... you DO NOT want to be booting from the internal HDD. The OS shouldn't be there.

So...
The external SSD should have:
- OS
- Applications
- Accounts (basic).

By "basic" accounts, I mean that you have moved "the big stuff" -- your large libraries of movies, music, and pictures -- to the internal HDD.
This can be easily done, even if the actual home folder remains on the SSD (where it should be).

A 1tb SSD probably ought to have 10-15gb "left free" for such things as temp files, VM space, etc.

But again, the OS will run much better from the external SSD, than from the internal HDD.

 

[gilby101]

A 1tb SSD probably ought to have 10-15gb "left free" for such things as temp files, VM space, etc.

What! Much happier with 20% free.

I could even get an external 2 TB SSD for not too much

Or even a 1 TB. Just move photos, music and videos to it (whatever consumes most space).

And, of course, make sure your backup disk is big enough to backup both SSDs.