IMac – Repurpose Fusion Drive – Booting from USB 3.2 Gen 2 SSD

bootcampimacssdwindows

iMac Retina 4k 21.5" (2019) 3GHz Core i5 with 8 GB RAM and 1TB Fusion drive.
Big Sur 11.2 booting from external 1TB Samsung T7 SSD, backing up to a NAS.
Questions:

Is the internal SSD (28GB?) active in this setup?
Can the Fusion drive be formatted and Windows 10 be installed on it using Bootcamp?
Can the Fusion drive be 'split' and the internal SSD 'fused' to the external SSD?

Thanks for any input.

Best Answer

Is the internal SSD (28GB?) active in this setup?

Your Mac was shipped with an 1 TB SATA HDD and a 32 GB NVMe SSD. So, you have two separate internal drives which were configured as a Fusion drive with macOS installed. You state in your question that you have an 1 TB Fusion drive, so I assume the internal SSD is active as part of the Fusion arrangement. You should be able to verify this by inspecting the output from the command diskutil list.
Can the Fusion drive be formatted and Windows 10 be installed on it using Bootcamp?

Here, I assume you mean using the Boot Camp Assistant to install Windows 10. In this case, the answer is no. You would be trying to install Windows 10 on a USB drive and the Windows 10 installer GUI would not permit this to occur. However, you can use the Boot Camp Assistant to download the Windows Support Software (the drivers), then you could install Windows 10 by using the Windows 10 installer CLI. For example procedures, see this answer.
Can the Fusion drive be 'split' and the internal SSD 'fused' to the external SSD?

You should be able use the internal SSD and external SDD to create a Fusion drive arrangement. You could even install Big Sur into this Fusion drive. I was able to verify this part of my answer by creating this arrangement in a VirtualBox virtual machine. I assume if this is possible in a virtual environment, then the same configuration would work with real hardware.

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IMac – New iMac (mid 2013) storage options

The PCIe flash storage will be faster than the SSD, but how much you'll notice that in the real world is questionable.
The PCIe card used in the new iMacs is the same (custom) stick-like form factor Apple uses in their other products.
You should get the 1TB or 3TB Fusion drive configuration if you want more than 256GB of storage and don't want a larger SSD. You could of course get an external USB3 drive to provide large storage if you prefer, or even get a USB/Thunderbolt external SSD.

The $200 for the fusion drive is expensive, but not insanely so. It will give the most noticeable performance boost of any possible upgrade on the iMac, unless you prefer to spend the money doing an all-SSD setup, which will still be very, very fast.

You're not going to find a compatible PCIe SSD for any less than Apple's upgrade cost. For example, OWC sells compatible SSDs for the MacBook Airs (http://eshop.macsales.com/shop/SSD/OWC/Aura_Pro_Air_2012) that may work, but I don't believe anyone has specifically tested it.

I will also note that opening up the current iMacs is more difficult than in the past, due to the laminating process on the screen to reduce glare, parallax and weight. It would be a false economy to buy a $2000+ computer, only to risk damaging it by opening it up for the chance to save $50. If external storage is not desirable and you want more capacity, go Fusion.

MacOS – Fusion Drive, Bootcamp and FileVault – with working Recovery HD

OS X Internet Recovery
Mac models introduced after public availability of OS X Lion include the ability to start up directly from an Internet-based version of the OS X Recovery system. OS X automatically uses this feature when the Recovery System on the hard disk isn't available (such as when your hard disk encounters an issue, or when your hard disk has been replaced or erased).

My setup is a Mac mini 2011 with a DIY Fusion drive (840 Pro + 1 TB Hitachi). The Fusion drive was built on 10.8 and then the machine was upgraded to 10.9.

diskutil list 
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         255.7 GB   disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage                         934.5 GB   disk1s2
   3:                 Apple_Boot Boot OS X               650.0 MB   disk1s3
   4:       Microsoft Basic Data BOOTCAMP                64.9 GB    disk1s4
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Fusion HD              *1.2 TB     disk2

When I press alt, I get three entries, Fusion, Fusion, Boot Camp. Either Fusion being selected boots the main OS. Bootcamp boots Windows.
⌘R boots local Recovery HD (not Internet Recovery). I have a choice of Wi-Fi, if I need Internet Recovery.

In your case, is it possible the Recovery HD is damaged?

Best Answer

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IMac – New iMac (mid 2013) storage options

MacOS – Fusion Drive, Bootcamp and FileVault – with working Recovery HD

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