Can you use two SSD’s as a Fusion Drive set?

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Bob Span @bob51

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Can you use two SSD’s as a Fusion Drive set?

I have been researching this issue for a while now. I am A+ cert. and have Google certifications also. I have disassembled, reassembled and repaired many a machines. This is not an issue for me.

I have the SATA thermal adapter cable, frame and new adhesive strips

The things stated here are true but the big question is "Will an SSD in place of the HDD portion of the Fusion drive work after installation?

As we know Apple, is very particular as to what will play nice with their hardware/software.

I have a 1 TB, 2.5 Samsung Pro 860 SSD to replace a Seagate ST1000DM003 HDD in a mid 2017 27" iMac, macOS 10.13.6. The SSD blade for the Fusion drive is the Apple custom 32 GB Samsung SSD on the logic board.

Any specific experience here, I would greatly appreciate. I am not interested in just adding external storage and high capacity blade storage is too expensive. Thanks in advance

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Dan @danj

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We did some tests a few years ago and found the smaller 32/42 GB Blade SSD’s just didn’t offer enough benefit in a Fusion set when mated with a SATA SSD. It was more beneficial as the boot drive and only holding the MacOS files and nothing more. Apps & data files would be held on the SATA drive.

I would strongly recommend replacing the blade SSD to a larger one to truly get the best out of your system. These small SSD’s used for Fusion Drives are just to limiting. You don’t need a massive drive, as an example 256 GB SSPOLARIS SSD. That way you can hold your apps in addition with your OS. It also gives your system enough free space for virtual RAM an application paging space.

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Andrew Stephens @doctorhappymac 평판: 13 2 · Answer 1 · 2020-08-05T00:20:39-07:00

You can add two SSD’s to create a fusion drive. However there are important caveats.

Apple list a specific set of terminal commands to create a fusion drive set. These do not work when using two SSD’s, the older set of steps easily found online at MacWord etc do work and will create a fusion drive from two SSDs.

However, Apple specifically block this configuration and the installers for both Mohave and Catalina will refuse to instal if you have two SSDs as they will see the array as a simple RAID setup and macOS no longer installs on RAID drives. You can instal High Sierra, this seems happy enough to work but any future upgrades will need to be done by cloning back and forth using 3rd party tools which is a pain.

The main advantage from using two SSDs is not going to be a lot of speed as the FD should be running from it’s SSD component most of the time (less so on post 2017 iMacs where the SSD was dropped from 128GB to 32GB (really???), however on 21in iMacs even fusion drives suffer from the awful spec drives Apple used in these so you will gain some speed but more importantly reliability.

So swings and roundabouts.