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iMac 2019 with 1TB Fusion drive is incredibly slow to boot

JohnnyWalker

JohnnyWalker

macrumors member
Original poster
Feb 25, 2005
73
61
I have a 2019 iMac with a 1TB Fusion drive running Big Sur 11.2.3. The machine runs fine most of the time... until I have to open an app. Or worse, reboot the machine. It's no exaggeration to say that it can take 40 mins to fully finish booting (ie. re-opening the apps I use: Chrome, PHPStorm, Terminal, Music, Photoshop, Dropbox, Mail).

40 mins.

I know that's a fairly large amount of apps, but probably not much more than the average web developer. I can use the machine while it's re-opening the apps I use, but it takes 40 mins before they're all fully responsive and available to me.

Is this expected behaviour?

If this isn't expected behaviour, what can I test to see what's going wrong?

Screenshot 2021-04-04 at 13.46.52.png
 
The fusion drive trying to run Big Sur is "what's going wrong".

Over in the m-series sub-forum, there's a long-running thread about unbelievably high disk writing on the m-series Macs. You can see it here:
forums.macrumors.com

ssd swap - high usage of Terabytes Written

Please read the update at the end of this post. Hi, I have Mac mini m1 256/16 for almost 8 days. After those 8 days I can see 0.9 TB written. From what I found on the web this ssd should last for ~~150 TBW. After 8 days I have 0.9 TBW :) I checked on my MacBook Pro 13" from 2018, 256/16 as...
forums.macrumors.com forums.macrumors.com

I'm wondering if the out-of-the-ordinary disk swapping may be occurring on Intel Macs running Big Sur, as well?

This could impact booting and running on Macs with slower drives.
And any Mac with either a platter-based drive (only) or a smaller fusion drive (which has only a 32gb SSD portion) may be impacted by this.

The solution is to buy an EXTERNAL USB3 SSD, connect that, and set it up to become the new boot drive.

You could use either an "ordinary" USB3 SSD (which will give you reads in the 420-430MBps range), or...
Buy an "nvme" blade SSD and a USB3.1 gen2 enclosure. They just snap together. One of these will give you reads in the 700-900MBps range.
 
Last edited:
Short term solution: make yourself an external USB 3.x SSD and use Carbon Copy Cloner to clone everything over. Set it as the boot and get back to work. If you have important data on there and no backup I would do this *immediately*. And I would use the machine as little as possible until that is complete. You could just purchase a pre-configured external SSD if you wanted, but building your own is incredibly easy (buy case, but drive, snap together, plug in, format) and will save you a few bucks.

Possible hardware causes: What you describe is very common on older fusion drive arrays when the HDD begins to fail; the machine can become almost unbearably slow but actually continue to function. It would be unusual, but by no means impossible, that your machine is experiencing a premature storage failure.

Other possible causes could be software or drive-structure corruption. Try running Disk Utility to check the drive. You could boot externally, break apart the fusion drive, test each component (SSD and HDD) individually, and then rebuild the fusion array if you wish. This is a painful process - OWC / Macsales has a good guide. Reinstall the OS and use Migration Assistant to migrate your data back from your external. If you are not having any hardware failures that should resolve things.

But ultimately the most important thing is your data. Worry about that first and everything else afterwards.
 
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Apple should be embarrassed for ever releasing 1TB Fusions with the 32/28GB blade drives. Simply not even big enough to load the operating system. A cheap solution to compete in the market place with cheap PC computers.
 
panjandrum said:
Short term solution: make yourself an external USB 3.x SSD and use Carbon Copy Cloner to clone everything over. Set it as the boot and get back to work. If you have important data on there and no backup I would do this *immediately*. And I would use the machine as little as possible until that is complete. You could just purchase a pre-configured external SSD if you wanted, but building your own is incredibly easy (buy case, but drive, snap together, plug in, format) and will save you a few bucks.

Possible hardware causes: What you describe is very common on older fusion drive arrays when the HDD begins to fail; the machine can become almost unbearably slow but actually continue to function. It would be unusual, but by no means impossible, that your machine is experiencing a premature storage failure.

Other possible causes could be software or drive-structure corruption. Try running Disk Utility to check the drive. You could boot externally, break apart the fusion drive, test each component (SSD and HDD) individually, and then rebuild the fusion array if you wish. This is a painful process - OWC / Macsales has a good guide. Reinstall the OS and use Migration Assistant to migrate your data back from your external. If you are not having any hardware failures that should resolve things.

But ultimately the most important thing is your data. Worry about that first and everything else afterwards.
Click to expand...

Excellent advice. I ran Disk Utility First Aid and it found no issues. Shrug.
 
JohnnyWalker said:
I have a 2019 iMac with a 1TB Fusion drive running Big Sur 11.2.3. The machine runs fine most of the time... until I have to open an app. Or worse, reboot the machine. It's no exaggeration to say that it can take 40 mins to fully finish booting (ie. re-opening the apps I use: Chrome, PHPStorm, Terminal, Music, Photoshop, Dropbox, Mail).

40 mins.

I know that's a fairly large amount of apps, but probably not much more than the average web developer. I can use the machine while it's re-opening the apps I use, but it takes 40 mins before they're all fully responsive and available to me.

Is this expected behaviour?

If this isn't expected behaviour, what can I test to see what's going wrong?

View attachment 1753432
Click to expand...
One decade old advice I can give is this, - always lag intentionally one OSX System behind. I suspect Big Sur is the elephant in the room here. You need to know, Big Sur is not an ordinary version. This time we talk about a transitional OSX. Last time this happened was 2006 when Apple switched from ppc to intel. This will be a long and painful birth with many unknowns and risks. My advice: Go back to Catalina and let others do the Beta testing.
 
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