Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.


Question: Monterey and Fusion Drive

For those who have an iMac late 2015 with 1TB Fusion Drive (32GB SSD), this is just a small note to let you know that, contrary to Big Sur, Monterey runs smoothly with normal booting times (around 40-50 seconds). On my system, Big Sur rendered my iMac painstakingly slow and unusable and I had to revert to Catalina.

Yesterday I upgraded from Catalina to Monterrey and everything is fine. Hope this information is helpful and useful to anyone.

Posted on Oct 28, 2021 11:31 AM


Oct 28, 2021 11:40 AM in response to claudiafromlisboa In response to claudiafromlisboa

Thanks, this is good news. I had the same issue with an iMac from 2019 with a Fusion drive. My solution was to use an external SSD drive through the speedy thunderbolt 3 port. I have used this SSD as bootdisk with Big Sur and it was smooth. Big Sur was indeed unbearable from the Fusion drive.

Monterey is for some reason unbearable slow from the external SSD. I'm making backups as I speak to try and re-install Monterey on the Fusion drive, to see how that goes.

Oct 28, 2021 11:40 AM

Reply Helpful (2)

Oct 29, 2021 2:49 AM in response to Mac_Hammer_Fan In response to Mac_Hammer_Fan

Reporting back a day later. I'll be complete so this information can possibly help others.

My system:

iMac (Retina 5K, 27-inch, 2019)

Processor 3,6 GHz 8-Core Intel Core i9

Memory 48 GB 2667 MHz DDR4 [by manual upgrade]

Videocard Radeon Pro 580X 8 GB

Harddisk Fusion drive 3TB

External hard disk SanDisk Extreme SSD 1TB

Factury situation:

The iMac came with macOS (Catalina?) pre-installed on the Fusion drive.

Moving forward:

I upgraded to Big Sur on the Fusion drive but the system became stuttery. It was suffering short halts and made working super annoying. I read a lot of info online and found a promising cost-efficient solution in booting from an external SSD.

Until last week:

I had Big Sur installed on and booting from the external SSD drive, attached through Thunderbolt 3. This was working very smooth, the external SSD was notably faster than the internal Fusion drive. The only downside was that during booting, the SSD was still powering on and therefor could not be found at boot. To work around this I had to hold Alt/Option every boot to load the boot manager and pick the boot drive manually, because usually it would be live just half a second too late for the normal boot sequence. Once booting however, it was fast.

Last week:

I upgraded to Monterey on the external SSD, installation went ok, but the reboot after finalizing took 3 hours (!!!) to complete. I only gave it this much time cause I didn't want to crash it during installation, at some point I didn't expect it to continue, but in the end it did. Monterey was installed and booting, however, every boot since took about 30 minutes. Super slow.


I read online that there are issues with Monterey on non-factory hardware. So I decided to try installing on my internal Fusion drive rather than on the external SSD. I had however used the internal Fusion drive as a data disk, and had to backup 2,5 TB of data before I could do this. I found 4 TB worth of disk space spread out over old USB drives, and backed up everything manually on these drives.

After completing and securing my backup I created a Monterey portable installer following one of many (easy) guides on the web on one extra external USB drive. This was done in a few minutes.

I shut down the machine.

I unplugged all external drives and third party apparatus.

I connected the Monterey installer USB drive and booted the iMac holding down Alt/Option to then pick the Installer as boot drive.

The installer boots to a welcome and I used the here provided Disk Utility to wipe all data from the internal Fusion drive.

Now ready to install Monterey on the internal Fusion drive.

The installation succeeded in less than 20 minutes. Nice, this is faster than it went before when upgrading Big Sur to Monterey on the external SSD.

Booting Monterey on the internal Fusion drive goes as snappy as one would expect, booting in a few minutes or less!

Now, I read somewhere that people having issues with slow booting Monterey on SSD drives (mostly MacBook users) fixed their issues by installing on the original hardware and THEN reverted back to their upgraded non-factory hardware. The idea is that the Monterey installer recognizes factory hardware and only then upgrades EFI firmware, once this upgrade is done, Monterey is supposed to run snappy on whatever hardware installed.

So for the ultimate test, I reset my iMac and boot again from the external SSD drive with a clean install of Monterey on it, to see if this installation (that was still on the drive) would now load faster.

Well, it didn't. It was still taking about 30 minutes to boot from the external SSD.


So, I'm keeping my Monterey installation on the internal Fusion drive. I've now migrated my installation from the external SSD to the Fusion drive using the Migrate assistant in Applications/Utilities. This worked as a charm.

[Why? Cause I had in the meantime re-installed and configured all my apps etc]

I wonder if I'll keep my boot speed on the Fusion drive installation as I move forward copying back terabytes of backup data from the external USB drives to the internal Fusion drive, but I'll have to see.

For now: I strongly suggest installing Monterey on your stock hardware! The Fusion drive (I have the 3 TB variant) seems to work great so far!


Oct 29, 2021 2:49 AM

Reply Helpful (1)

Oct 29, 2021 2:54 AM in response to sjogro In response to sjogro

Another configuration to consider, I thought of too late myself, is to split the internal Fusion drive into SSD and HDD manually [there are guides online] and use only the pure SSD part for the system installation, assuming that any expected sluggishness comes from miss-management of data across the Fusion drive.

This will probably be my last resort if I end up running into trouble. I hope not though.

Oct 29, 2021 2:54 AM

Reply Helpful

Dec 10, 2021 12:38 PM in response to GtrBruno In response to GtrBruno

It works!!

I have an iMac 21.5” 4K 2017 / 3ghz core i5, / 8gb Ram, fusion drive (32gb ssd + 1tb hdd)

  • I repaired my Fusion Drive from separate partitions.



  • then Erase fusión drive and restart computer.
  • install OS from the factory (for ejample : sierra in my iMac)
  • then update to monterey.

thats it!

Monterey runs smoothly !

I think I will upgrade my Ram memory but is good and normally speed for now.

Dec 10, 2021 12:38 PM

Reply Helpful (2)

Jan 15, 2022 3:15 AM in response to claudiafromlisboa In response to claudiafromlisboa

Hey man! Thanks a lot for the heads up. I have been waiting for someone to post this good news. Had to downgrade to Catalina after big sur sucked on fusion drive (IMac 21 inch 2019 1TB fusion drive). After your post i will now proceed with upgrade and post my feedback after done. Thank you once gain and all other posters here.

Jan 15, 2022 3:15 AM

Reply Helpful
User profile for user: claudiafromlisboa

Question: Monterey and Fusion Drive

Welcome to Apple Support Community
  • A forum where Apple customers help each other with their products. Learn more.
  • Sign up with your Apple ID to get started.