External SSD boot drive for 2017 iMac

[Kurt Cowling]

I'm interested in having my 2017 iMac boot from an external SSD rather than the internal Hybrid drive. I'd probably get an OWC Envoy Pro EX. I really don't want to open up the iMac and replace the internal drive if I don't have to. Right now I'm on Catalina but plan to go to BigSur when all my software is ready.

Anything about this that is problematic? Will I have trouble updating/upgrading OS when it's on an external drive? I remember there being some discussion here but can't seem to track down the exact conversation.

Also, I will probably want to keep my Apple Music library and photos on the hybrid drive to save space on the SSD. I have no experience with Terminal or the like. Hopefully that's not too complicated.

Thanks for any insights!
--Kurt Cowling

[mikehalloran]

Hi Kurt, since you have a Fusion drive the best performance really is opening it up, replacing the internal SSD with a fast NVMe 3 x4 blade like the 970 EVO. Your iMac has a Samsung blade inside.

$349 for 2TB https://smile.amazon.com/Samsung-970-EV ... ref=sr_1_4
plus a $15 pin-out adapter. https://smile.amazon.com/Sintech-Adapte ... ref=sr_1_4

The OWC Aura Pro X2 has the correct pin-out but costs $85 more.

Then, if you need more storage, install a SATA III SSD in the remaining space, 1, 2, 4 or 8TB. $90–$750. You can have the two configured as a monster, all solid state fusion drive or as separate drives.
https://smile.amazon.com/SAMSUNG-870-QV ... ref=sr_1_3

Installation runs around $75–$100 here in the Silicon Valley (it doesn't take 20 minutes + data transfer for an experienced tech). You might want to call around.

The only 2 externals I can recommend for booting are true Thunderbolt 3. Anything else is slower than your 2017 iMac (USB 3.2 etc.).
4TB https://eshop.macsales.com/item/OWC/TB3ENVP40/
2TB https://www.amazon.com/Samsung-Portable ... 07GBWZJFG/


When you consider that the least expensive 2TB external is $600, it makes sense to consider replacing that tiny blade in your iMac. I forget if the original blade is 64GB or 128GB on a 2017 Fusion.

[Kurt Cowling]

Thanks so much for your insights. I’ll look around and see if there’s a tech in my area that can do the internal replacement.

Sorry I didn’t reply sooner. I didn’t get an email telling there was a reply and then I’ve spent most of the week severely under the weather.