Format and install OS on New Internal SSD on iMac 27" late 2012

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Format and install OS on New Internal SSD on iMac 27" late 2012

iMac late 2012 - 32GB RAM

Hi there. Today I installed a new Crucial MX SSD 1TB drive in my iMac. Was an easy job removing the screen and all. The hard part comes now installing the OS and I thought that would be easy :-)

I booted my iMac from a Samsung external SSD drive to make some screen shots to show how the internal drive looks like. It's split up for a reason and what I think I am missing is the Fusion drive (I am not familiar really how that works). Now there is 1TB and 121,33 GB as per enclosed photos and I have no clue how to continue on which drive I should install Catalina. I know the trick with Recovery and I have the necessary Backup and all that but it feels I am no sure about how to continue and I think I am missing/misunderstanding the Fusion drive function for some reason.

Please help me how to proceed - thanks so much

Kind regards Erwin

iMac 27″, macOS 10.15

Posted on Dec 12, 2022 6:50 AM

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Answer 1

Top-ranking reply

a brody

Level 10

84,055 points

Dec 12, 2022 1:08 PM in response to ErnieBernie65

Unfortunately, you didn't get a true 100% SSD. Only 128 GB is set aside as SSD, while the rest is a platter spinning drive. The SSD portion is generally considered for OS only, but mapping the rest of the data to the rest of the drive is essential so you don't overflow the drive.

When Apple normally configures the drive as a fusion drive it usually is more transparent.

How to fix a split Fusion Drive - Apple Support

is probably the reference you need to work with.

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Answer 2

Dec 13, 2022 1:13 AM in response to a brody

Thanks so much for your reply. That worked for me and now the disc is how it should be. All data is back and the Imac works fine again.

However now I have to get some speed into the new SSD - Blackmagic Disc Speed Test shows only 200 for writing and 400 for reading which I thought would be around 600. I enabled the Trim function and also read about an input "fsck -fy" in Command - S boot to speed up but that gave an error for me. After Exit it booted normal again but still "slow" speed. Don't get me wrong, with the new SSD it's much faster then before but I read it should be even faster.

Any idea what to do or shall I make a new thread?

Thanks again

//Erwin

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Answer 3

a brody

Level 10

84,055 points

Dec 13, 2022 6:53 PM in response to ErnieBernie65

I'm not sure I would put too much credence towards speed tests. Mac OS X runs many background operations which delay speeds. http://www.binaryfruit.com/ DriveDX can more accurately determine the health of the drive. if fsck is not repairing things from single user mode or booted from a different drive, that normally can be either something really wrong with the directory or the drive.

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Answer 4

Dec 14, 2022 12:55 AM in response to a brody

Yeah you are right. This iMac is 10 years old after all and I should be happy anyway with the performance after the upgrade to SSD. It's a huge difference so for me it's case closed :-)

I checked out the DriveDX and both the Fusion and SSD show good performance. The lifetime left indicator for the Fusion Drive shows 71% but it's still green. All good in my opinion.

Thanks so much for your help

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Format and install OS on New Internal SSD on iMac 27" late 2012

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