Have an older lame iMac with a fusion drive? Boost it at absolutely no cost! No hardware change required !

[rin67630]

If you have an older lame iMac with a fusion drive, you can boost it at absolutely no cost!
No hardware change required !, no need to open the iMac !.

First of all perform in the Terminal:

Diskutil list

and check if the SSD part of your Fusion drive is 121 GB.

If it is a smaller one, sorry, that is not for you.
If you have a 121 GB SSD blade, you can really boost your iMac and make it fly whilst being ways more reliable:

We will split the fusion drive, install macOS on the SSD part , format the HDD hfs+ and move the user folder to the HDD, so your growing stuff will not clutter the small SSD.
You will need two 32 or 64GB SD sticks (useful anyway).

First of all, make a full backup of your current drive data. (this is something everyone ought to have anyway).
Then make a bootable install SD stick with your favourite macOS installation.
Then make another bootable SD stick with just macOS on it (both are something everyone ought to have).
Boot from it and...

-Reformat (erase) your fusion drive to ExFAT. This will break the Fusion drive and split it into a HDD and a distinct SSD.
-Reformat (erase( your HDD with hfs+ (macOS journaled case insensitive)
-Reformat (erase) the SSD with APFS.
-Install a clean macOS to the SDD.
-Boot from it.

(enjoy the fast boot)

-Migrate your apps (not your user data) from the backup to your new macOS.
-Boot from the new installation.
-Copy your user folder to the HDD.
-Move your user folder to the HDD location where you copied it*.
-Reboot
-Enjoy a turbo iMac, that is much faster and much safer** to use as before.
-Eventually move your user data from the backup to your new installation (a great opportunity to cleanup the mess).

*To move the user folder: System preferences Users and groups, go to your user, open the lock, right click on your user, select advanced options and change the user directory.

** why ist it much safer?
When only one of the 2 drives of a fusion drive is lost, everything is lost, and in case of APFS unrecoverably lost. APFS awfully hammers both the SSD with permanent overwrites and the HDD with a dreadly fragmentation. Causing them to fail prematurely.

At the opposite, my way is nice to both the HDD that will run hfs+ (mostly recoverable even after a failure) and to the SDD that will mostly be read, preventing it's wear.

Last but not least, a HDD carrying only your user data formatted hfs+ is mostly not noticeably slower to use than a SSD. It's the permanent head swapping between the zillions small files of an OS and the programs that makes the every-day's usage slow.

 

[Alvin777]

Yup, upgraded to them SSDs (NVME, SATA) , including the Time Machine (though wrong buy, I didn't know Time Machine needs 2x the capacity to work right- will save up for that).

Thanks again.

Thanks for taking time for this thread (8 year old iMac still has the best and maybe cheapest 5K screen, I'll recommend OWC to invent a mod chip to make it an external monitor for the upcoming M Macs w/ 2nm fab though it's tempting to just buy the amazing Apple Vision Pro coz' one can be very productive in it- it's essentially a 7k resolution 'eyesMac' :-D but the pixel count is even higher and more dense than Apple XDR 7k, also my upcoming room will be smaller, 40% smaller).

 

[rin67630]

Yup, upgraded to them SSDs (NVME, SATA) , including the Time Machine (though wrong buy, I didn't know Time Machine needs 2x the capacity to work right- will save up for that).

Time Machine works best with HDDs with hfs+, since it permanently writes and rarely reads.
For that job, rotating drives are ideal, speed does not matter and writes do not wear them.
The best option upgrading an iMac with a Fusion drive is macOS on the blade and keep the huge HDD for Time Machine.

 

[bigshoe83]

I am in the process of doing this procedure on my 2019 with Fusion Drive, hope all works out. Thanks for the detailed instructions.