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Want to upgrade 2013 iMac with Mountain Lion?

Racineur

Racineur

macrumors 6502a
Original poster
Jun 11, 2013
578
176
Montréal, Québec
Allo. I want to upgrade an old 2013, 27, i5 Mac with FusionDrive. Probably to Mojave. ML is unusable now. I think I have to upgrade to High Sierra before, isn't that right? I'd like to wipe out the FD too. How can I do that before starting the upgrading process? What will happen to the Fusion Drive? Will the formatting erase the 128g integrated SSD used to nest the OS? Should I just let the High Sierra Installer do the installing, then upgrade to Mojave? This iMac boots with Mojave or Catalina on external SSD for a while now. But I'm curious to know if the Fusion Drive would do a good job with Mojave or Catalina. Thanks for helping.
 
If it’s the 128 SSD fusion, I would separate it. Make yourself a bootable copy of High Sierra, boot to recovery, erase and defuse the disks, install High Sierra, then higher if you want.
This all assumes you have a backup.
 
According to everymac.com, a 2013 iMac can go up to 10.15 "Catalina".

I agree with Mr. Brightside. For the best speed increase, SPLIT the fusion drive into SSD and HDD "separate" drives.

Then, boot to INTERNET recovery (you might have to do this to split the drives).

Internet recovery should offer you Catalina, install it onto the SSD.

Then, you could set up the SSD this way:
- OS (for fastest speed)
- Apps
- Accounts ("bare-bones", keep large libraries of music, movies, and photos on the HDD).

You will have to be mindful as to how you "manage" the boot SSD, to keep enough free space on it for the best speed. Not really that difficult to do.
 
This is an unofficial route, but just to say, this week I updated my 2008 (!) Mac Pro to Monterey using the below process, and it was utterly seamless. Took about an hour and just required me to follow their steps to the letter. I didn't push it to Ventura, I thought I would take the final version of the last operating system so that all the kinks had been worked out but seriously, it works like a dream. I couldn't be happier; these guys are stars at keeping unsupported macs on their feet. Check your configuration beforehand, they seem to suggest iMac 2013 models are covered.

 
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Fishrrman said:
According to everymac.com, a 2013 iMac can go up to 10.15 "Catalina".

I agree with Mr. Brightside. For the best speed increase, SPLIT the fusion drive into SSD and HDD "separate" drives.

Then, boot to INTERNET recovery (you might have to do this to split the drives).

Internet recovery should offer you Catalina, install it onto the SSD.

Then, you could set up the SSD this way:
- OS (for fastest speed)
- Apps
- Accounts ("bare-bones", keep large libraries of music, movies, and photos on the HDD).

You will have to be mindful as to how you "manage" the boot SSD, to keep enough free space on it for the best speed. Not really that difficult to do.
Click to expand...
Hello to you Fshrman. I did ad you indicated. From an off iMac with Mountain Lion. Restarted and Booted up in Inernet Recovery Mode. Was presented with the option of reinstalling Os being Catalina. I'd be happy with Catalina. Knows that. But what assured me Catalina will be installed on the 128 SSD and progs and files n the 1Tb spinning HD. That's truly what I want be it Catalina or else. Again: how t make sure the Catalina installer will not "fuse" the two disks? As for splitting the Fusion Drive, not have big faith in this. Near finish line but not quite there yet. Thanks, Let's be patient.
 
Your post is confusing. If you have already split the FD, and name each SSD and HD for example and direct Cat to install to the SSD, it will NOT re-fuse.
 
Sorry for that. Let's go again: I bought my 2013 iMac new. It came with a 1tb Fusion Drive and Mountain Lion. What I understand of FD is the OS resides on the SSD and the files on the 1T HD. I do not know how to split a Fusion Drive and don't think about doing it. I learned it could be done just few days ago. Me, I just want to upgrade Mountain Lion to a more recent OS with the assurance the new OS being Catalina will be installed on the SSD portion of the Fusion Drive. I a nutshell: the same installation as Mountain Lion right now. BTW: I boot this Mac from an external SSD with Mojave. Is that less confusing? Thanks.
 
  1. The Fusion Drive is meant to intelligently allocate things to the SSD-I believe the OS is exclusively or mostly stored there, but I am not certain there is a solid answer. https://en.wikipedia.org/wiki/Fusion_Drive
  2. Ok, you should not proceed with splitting it. It was a suggestion, not a requirement.
  3. This is how FD should work, I would proceed with the install.
  4. That makes a big difference. Ignore the recommendation of splitting and upgrade the external SSD to Catalina. The FD isn’t involved with that.
 
Let's see here.

You are booting running from an external 1tb SSD with Mojave.

The internal fusion drive is 1tb and has Mountain Lion on it.

Is this correct?

So...
What do you want to do?
Is there stuff on the internal fusion drive that IS NOT on the external [boot] SSD?

WHY I'm asking:
I would suggest that you make the internal fusion drive "the backup" of your external boot SSD.
That way, if the SSD were to fail, you'll be able to immediately switch to the fusion drive and KEEP GOING.

This is VERY easy to do, it will cost you nothing.
Just download SuperDuper, which is free to use for this purpose.
It will "clone" the contents of the SSD to the fusion drive, after which the fusion drive will be AN EXACT COPY of the SSD.
(but remember, doing this wipes out whatever was previously on the fusion drive -- that's why I asked if there was anything on it that might need to be saved elsewhere)

You can periodically update the clone, to keep it "up to date" with the SSD.
SSD's -can- fail, and when they do, it's often with NO WARNING at all. They just "disappear".

You want to be protected against something like that.
 
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