Fusion drive SSD partition filling up too fast for HDD?

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Level 1

19 points

Fusion drive SSD partition filling up too fast for HDD?

I have a problem with two 2019 iMacs.

Two different users working at a magazine have both experienced this issue.

Certain macOS programs as well as Photoshop are reporting either out of disk space or scratch disks are full.

But there’s actually 36 gigs free on the Macintosh HD. (The internal fusion drive is the only connected hard drive) Other programs are grinding to a halt, networking operations are failing, etc.

Nothing is hanging in activity viewer, No obvious errors in console. There’s plenty of disk space free and we removed another 10 gigs just to be sure.

Tried starting up in safe boot and restarting again normally.

My theory is the fusion drive is not migrating new files being synchronized by onedrive to the HDD fast enough. And therefore the little SSD is filling up even though the volume shows there’s 36 gigs free.

So any programs that are accessing the SSD drive partition think the system is out of space. There is no obvious way to control or to see any statistics or information about how or when files are moved from one drive to the other In the fusion magic process and feel totally helpless.

How can I solve this problem? How can I make sure the SSD drive has enough space for the programs to function?

And this is not the “split drive“ problem I’ve seen other people talk about

Can anyone confirm or give any advice? Do I just need to wait for the macOS to finally catch up and move things over so there’s enough space for Photoshop to launch and other macOS programs to function properly? How do I fix this?

Posted on Apr 17, 2020 1:30 PM

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Answer 1

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BDAqua

Level 10

239,375 points

Apr 17, 2020 4:05 PM in response to Fluk3

Yes, you basically have it, but also Scratch Disks complicate things since the SSD part of the Fusion Drive loads the Most used files up to it's size limit, while trying to make space for the OSes need for VM, then OSX is constantly trying to Defrag the Larger files on the Drive. So we have several things searching & contending for the .036% chance of being near a free Sector to use... then the Memory gets squeezed trying to swap all these things requiring more VM to even store the pointers to the VM.

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Answer 2

BDAqua

Level 10

239,375 points

Apr 17, 2020 2:29 PM in response to Fluk3

Just a note 36 GB Free space would be nothing if say you have 32 GB of RAM.

EtreCheck is a simple little app to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac.

http://www.etresoft.com/etrecheck

Pastebin is a good place to paste the whole report...

https://pastebin.com/

Or use the paperclip at the bottom of a Reply to attach the full report here. :)

Workable but harder for me to work with...the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck.

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Answer 3

Fluk3 Author

Level 1

19 points

Apr 17, 2020 3:06 PM in response to BDAqua

True, 36 GB is not much space left at all on a 1 TB hard drive. (Fusion drive or otherwise) It is far below the minimum 10% I usually advise to be free.

The user does have 32 gigs of RAM and I made sure that there is plenty of memory free, no swapfile was being used, etc..

Now I’m thinking that a paltry 36 GB free, while not nothing, is too much overhead for the fusion drive to move files around efficiently.

I love ertacheck and I subscribe to the pro version with the power package.

Sadly, I can’t run it right now because I’m diagnosing them remotely and the machine is so bogged down that no screen sharing app can connect to view and manage them. So I’m unable to run ertacheck.

As familiar as I am with etracheck I don’t think it’s going to address the fusion drive in so far as how it manages what data gets moved to which drive and when.

I’m hoping that I can manage to get them to de-synchronize 100 GB+ out of their onedrive and that should be enough for things to right themselves.

I really wish there was some sort of “best practices” guide for how the fusion drive works it’s magic shifting of files between drives and what their tolerances are. But what I think I’m learning is when space gets too low, that magic file swapping between the partitions fails to some degree.

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