Fusion drive as storage?  



Yesterday's lack of a new iMac announcement has me looking anew at my upgrade options. I’m <still!> running a 2007 iMac in my home office. It’s got an SSD, and it’s served me well. I setup a 2017 3.0ghz/16gb/1tb HDD iMac recently for a friend, and was shocked at how slow it seemed in comparison to my 11 year old machine. That hard drive is amazingly poky.
I had hoped that Apple would start shipping iMacs with a less expensive SSD option ($700 for 1tb, really?! And only 500gb available for 21.7” machines), or do away with the HDD option altogether, but no such luck. I’ve installed SSDs in plenty of machines, but the newer iMacs give me pause.
In lieu of a built in SSD, I purchased a (used) LaCie Rugged 2tb Thunderbolt/USB-C HDD, took the drive out, and replaced it with a 1tb Crucial M500 1tb SSD. My plan is to use this as the startup drive via USB-C/Thunderbolt 3.
So, with all that laid out, my actual question is, does it make any difference whether I order the model with an internal HDD or a fusion drive? If I use the internal drive as storage, is there any speed advantage to having a fusion drive? Or does it only take advantage of its onboard cache when used as a startup drive? I could also use the internal drive as my backup clone, in which case speed only matters if my external SSD fails.

This topic was modified 7 months ago by blocktek
3 Answers

I have only ever used a Fusion Drive as the startup disk, but given that you can "build" one via Terminal commands I cannot see any reason why it would not work as a non-startup disk.

Old UNIX Guy


Agree with @kevinbuterbaugh — this should work fine, and I think your plan is a smart one, @blocktek

But will there be any speed advantage in this configuration? At least enough to justify the extra cost?


I'd say the answer to that is going to heavily depend on what you're using the storage for.  Again, I've never used a Fusion Drive for anything other than a startup volume.  I can tell you that in that scenario it does help significantly.  Of course it's not as good as a pure SSD.

I had a mid-2011 27" iMac that formerly had only an internal HD.  I installed an SSD in it (behind the DVD drive) and turned the SSD and HD into a Fusion Drive via Terminal commands.  I can tell you that for that configuration it cut my boot times in half.

I know a lot of people are ambivalent about Fusion Drives, or maybe even a little scared about using them, but I think that while they're not nearly as good as pure SSD's, they're also a ton better than just pure HD's...

Old UNIX Guy