Clean install of Big Sur or booting from external SSD?

[pburtsoff]

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]

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]

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 )

 

[dcmaccam]

Also clamping the SSD to the stand with, if possible a thermal strip would provide extra heatsinking for the SSD if required. I used a couple of tie-wraps.😁

 

[dcmaccam]

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]

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.