Why do I have 2 Catalina-Data partitions?

lend27 · Nov 10, 2019

As you can see in the screenshot below, for some reason I ended up with 2 Catalina-Data partitions.
I also have a Mojave install and that only has one data partition.
Any idea what I should do with the extra partition?
As you can see, the Mojave install only has one data partition.
Any ideas guys?

Thanks!
Len

Screen Shot 2019-11-10 at 9.42.59 AM.png

remington · Nov 10, 2019

Did you reinstall Catalina?

trs96 · Nov 10, 2019

This is normal in Catalina, nothing to be concerned about. It's Apple's way of doing things since the OS is read only and kept separate from the data partition which is read/write.

lend27 · Nov 10, 2019

trs96 said:
This is normal in Catalina, nothing to be concerned about. It's Apple's way of doing things since the OS is read only and kept separate from the data partition which is read/write.

But isn't it normal to just have one data partition, not two?

lend27 · Nov 10, 2019

remington said:
Did you reinstall Catalina?

Yes I did, but I formatted the disk in APFS prior to the reinstall.
Is there one that I can safely delete?

lend27 · Nov 10, 2019

trs96 said:
This is normal in Catalina, nothing to be concerned about. It's Apple's way of doing things since the OS is read only and kept separate from the data partition which is read/write.

And why do they have such vastly different amounts of data on them?

trs96 · Nov 10, 2019

lend27 said:
And why do they have such vastly different amounts of data on them?

Each slice (s1) of the Mojave and Catalina drives are about the same size in KB. The large system data partition on the Catalina drive is where all the stuff you add post install goes. That's why it's so large at 180 GB. I'm not sure what Apple puts on s1 of each disk but I'm interested to know if you look into that. The 10.8 GB disk4s6 is where all the read only Catalina system files reside.

itwas · Nov 11, 2019

lend27 said:
And why do they have such vastly different amounts of data on them?

apple use "firmlink" to link together two volumes (system volume and data volume) as one single volume, something similar to unix symbolic link

for example, both system volume and data volume have the /Applications folder

system volume /Applications folder is always empty
data volume /Applications folder is for the users to store the user apps (non-system apps)

system volume /Applications <-- firm link --> data volume /Applications = /Applications

firm link bond together this two /Application folders as a single /Application folder

you don't need to know how it works, Catalina macOS take care all about this

lend27 · Nov 11, 2019

itwas said:
apple use "firmlink" to link together two volumes (system volume and data volume) as one single volume, something similar to unix symbolic link

for example, both system volume and data volume have the /Applications folder

system volume /Applications folder is always empty
data volume /Applications folder is for the users to store the user apps (non-system apps)

system volume /Applications <-- firm link --> data volume /Applications = /Applications

firm link bond together this two /Application folders as a single /Application folder

you don't need to know how it works, Catalina macOS take care all about this

I guess my main question is why do I have 2 Catalina-Data volumes and can I delete one? (which one?)

ghorwith · Nov 11, 2019

As of the next release, although the OS maintains both volumes (ie Catalina and Catalina - Data) you'll only see one volume (ie Catalina) on the desktop and sidebar. As described above the OS uses a firmlink to make 2 volumes appear as 1. If you explore with disk utility or efi agent, you'll see both volumes.

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Why do I have 2 Catalina-Data partitions?

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