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pburtsoff

macrumors newbie
Original poster
Nov 28, 2020
1
0
I have a 2015 5K 27-inch iMac (3,2 GHz Quad-Core Intel i5, 16GB RAM) with a 1TB Fusion Drive.

macOS Catalina was running smoothly, but ever since I upgraded to macOS Big Sur, I've experienced general sluggishness, slower than usual startup and app launch times etc.

As an experiment, I installed Big Sur onto an external Samsung T3 SSD-drive (connected via USB 3.1) and booted the iMac using it instead of the Fusion Drive. It's lightning fast!

Now the question is: Should I wipe the Fusion Drive and attempt a clean install of Big Sur to see if it makes a difference or just keep using the external SSD as a boot drive?

I would prefer to keep using the Fusion Drive and not rely on an external drive, of course.

Thanks in advance for your insights!
 

paddylaz

macrumors member
Sep 18, 2012
72
72
I have a 2015 5K 27-inch iMac (3,2 GHz Quad-Core Intel i5, 16GB RAM) with a 1TB Fusion Drive.

macOS Catalina was running smoothly, but ever since I upgraded to macOS Big Sur, I've experienced general sluggishness, slower than usual startup and app launch times etc.

As an experiment, I installed Big Sur onto an external Samsung T3 SSD-drive (connected via USB 3.1) and booted the iMac using it instead of the Fusion Drive. It's lightning fast!

Now the question is: Should I wipe the Fusion Drive and attempt a clean install of Big Sur to see if it makes a difference or just keep using the external SSD as a boot drive?

I would prefer to keep using the Fusion Drive and not rely on an external drive, of course.

Thanks in advance for your insights!
Clean install all the way. My MacBook 16 was sluggish after upgrading from Catalina. Made the effort with a clean install, everything perfect now.

Also using an external drive as your boot is just......ugly
 

Airsculpture

macrumors 6502
Oct 14, 2020
303
76
I did both. I have a tiny 500GB SSD behind my iMac ( can't even see it ) and I did a clean install of Big Sur from Internet Recovery and my iMac is problem free ( apart from those inherent with Big Sur ) and running like a dream

I left my internal 1TB drive with its Catalina install alone and just use it for extra storage ( or will do if the SSD starts to get tight )
 
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dcmaccam

macrumors regular
Sep 14, 2017
179
21
West Coast of Scotland
Would installing Big Sur on an external drive change anything on Bios of my 2019 iMac during installation. I mean something that may cause problems if I decided to reboot the machine back to Catalina on the Fusion drive. I was wanting to tryout Big Sur to see how it went before committing. I have decided on maybe trying a 500GB Samsung T7.
 

Airsculpture

macrumors 6502
Oct 14, 2020
303
76
I can boot to either the external SSD with Big Sur, the internal disc drive with Catalina or another external SSD which I was running Catalina on with no issues. It is seamless.
 
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