VMware Fusion slow I suspect fusion disk on Mac

[charliektm400ex]

For a little while my installation of Fusion has been really slow. I have looked through lots of posts, and see quite a few questions about slow performance and helpful people are asking if the person is using a Fusion Drive, but I can't find anything that tells me what that problem is, and how to solve it.

On my computer I am using a Fusion Drive, and when VMWare is running I can hear the drive working.

I'm using OSX 10.15.7.  8G of RAM and 1TB fusion disk on  a 6 core 2019 iMac

Fusion 12.1.0 2G 2 processor cores

[wila]

Hi,

That helpful person would be @ColoradoMarmot 😉

IIRC then for a Fusion drive, the way to speed up things is to use the single file virtual disk instead of the virtual disk format with disk slices. This is almost the only scenario I can imagine that actually benefits from this particular format.

The reasoning here would be that the single big file prevents the data from ending up in the SSD cache and thus heavily fragmenting the virtual disk.

You will probably also be better off by putting the VM in a HFS+ partition instead of a APFS one.

I hope that Doug will correct me if anything I said is misremembered.

--
Wil

[ColoradoMarmot]

You've got it exactly right.  The fusion drive will 'age out' portions of the virtual disk to the spinning drive, and the have to move them back to the SSD as they are accessed - it's both the spinning disk and the move back and forth that appears to cause the issue.  The 'one big file' workaround helps if the VM is regularly used, but it can actually make it worse if it's infrequently accessed as the entire VM would be moved to the metal drive.

APFS on the boot drive also snapshots for time machine backups, which likewise can cause performance (on Fusion/spinning drives) and  apparent free space issues (on all drives).  

If the OP's machine has a USB C port on it, a solid workaround would be to get a Samsung T7 external SSD and run the VM's from there (I do that all the time, and it's really snappy).  If so, then a good backup system is highly recommended (and a pointer back to vimalin to you Wil!)

[charliektm400ex]

Thanks to both of you for the help.

I'm working towards getting an external SSD, but because of time frames it will be mid January before it can happen.

I don't understand how to make the VM one big file. Can you point me to where I can see how to do that in the interim please.

Charlie

[wila · Accepted solution]

Charlie,

Certainly.
First shut down the VM.
Then go to the menu "Virtual Machines" -> Settings
Select the disk.

There's a checkbox "Split into multiple files", remove the tick in the checkbox.
Then click the "Apply" button.
It will move the split file disk into a single disk.

Note that if you have any snapshots open (this includes the Auto Protect feature) then you have to commit all snapshots before you can make the change.

Also note that once you have moved the VM to another -non Fusion- disk that I strongly recommend to get back to the split file virtual disk layout.

The virtual disk split file is really the best choice even while it may seem a bit illogical at first.

With split files you:

• get a better response, faster results when doing any VMware disk operation such as snapshots, shrink, compact, extend and defragment.
• have less chance of getting into a "all data lost" scenario when something bad happens such as running out of disk space as the split disk file scenario is much easier to repair than a growing single disk.
• don't need to have the full virtual disk size on free disk when committing snapshots

--

Wil