Where the Mac OS should be installed when I have a Fusion Drive On iMac?

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Where the Mac OS should be installed when I have a Fusion Drive On iMac?

I have a Fusion Drive on iMac 2017 that was running fine using Mac OS Big Sur. I wanted to try the OS Ventura so I have created a partition. I found Ventura made my iMac a bit slower than with "Big Sur". I decided to erase everything and restart over with Big Sur only. I found my iMac became too slow. I did some trouble shooting like free PRAM and got a bit better result. But I'm still wondering if I can have it running back as before. Ran the disk utility, found "Apple SSD SM0032L Media" above "disk1s2" that has 27.69 GB only. It is cannot be mounted. I could erase it if the OS must be installed on it since it is much faster, I'm assuming. Shall I do that? Thanks a lot in advance, the mess is already done.

iMac 21.5″ 4K, macOS 11.7

Posted on Mar 5, 2024 2:26 PM

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Answer 1

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padams35

Level 4

3,619 points

Mar 5, 2024 3:04 PM in response to rami.k

Please don't partition a fusion drive with the intention of dual-booting. The second partition will be pure HDD and run -much- slower. (I suspect you actually created a new APFS volume. That works better, but your system will run slowly the first couple of times you boot into one OS after running the other since files not recently/frequently used will get moved out of the SSD space).

Please don't try to erase disk1s2. It is one of the fusion drive components. Also 28GB isn't enough space to install MacOS. Big Sur and newer requires at least 45GB of disk space, and I would recommend having at least twice that. macOS Big Sur - Technical Specifications

Your best path forward will probably be to purchase an external USB-C SSD and install Ventura onto that. However I would suggest you first install Etrecheck, run the diagnostic collection, and post the results here using the 'additional text' posting option. That will let us check to make sure your Big Sur install is not suffering from a broken fusion drive or other common issue.

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Answer 2

rami.k Author

Level 1

14 points

Mar 5, 2024 7:04 PM in response to padams35

Thanks a lot Padams35 for your helpful answer. I thought about buying an external USB-C-SSD. But I was wondering first to solve the speed of "Big Sur". For suggested Etercheck, I'm going to download and share the report later. How to clean up all this mess? I have backed-up my data and nothing to lose. Is there anyway to bring this iMac disk exactly as it was?Thanks again.

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Where the Mac OS should be installed when I have a Fusion Drive On iMac?

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