2019 27" iMac - add new partition to internal SSD?

[pavinder]

My iMac is running Monterey.
After reading many reports of Sequoia not running smoothly on Intel machines, I thought I might create an extra partition on my internal SSD and boot from that to test it without erasing my Monterey installation. The 512GB SSD has about 100GB free.

How much space should I allocate to the Sequoia partition and what format should be used?
In Disk Utility, do I simply select the top-level folder in the sidebar and choose the partition option?

Thanks in advance for any advice.

 

[Bigwaff]

Consider installing Sequoia on external USB SSD drive instead. Leave your internal storage alone.

 

[tonmischa]

For the new system you should create a new APFS volume inside your existing APFS container. This new volume will share the free space with your existing installation. So no need to decide on a fixed size.

All you need to know is here:

Use more than one version of macOS on Mac - Apple Support

If you install a compatible macOS on an additional internal or external storage volume, your Mac can start up from either volume.

support.apple.com

 

[pavinder]

For the new system you should create a new APFS volume inside your existing APFS container. This new volume will share the free space with your existing installation. So no need to decide on a fixed size.

All you need to know is here:

Use more than one version of macOS on Mac - Apple Support

If you install a compatible macOS on an additional internal or external storage volume, your Mac can start up from either volume.

support.apple.com

Thanks very much - this is exactly what I needed

 

[pavinder]

Consider installing Sequoia on external USB SSD drive instead. Leave your internal storage alone.

Yes, this makes sense to ensure everything is kept separate so my current setup remains intact.
Unfortunately I don't have a spare SSD to use, and the external HDDs I have run very slow as boot drives.

 

[Fishrrman]

Agree with waff above.

I have always used external drives (SSDs in recent years) on which to "experiment" with new OS releases BEFORE I "commit myself" to them by installing them onto the internal drive.

My recommendation is to get a Crucial X9:

https://www.amazon.com/Crucial-1TB-Portable-SSD-CT1000X9SSD902/dp/B0CGW1FQV4/ref=sr_1_1?crid=848C961OXW7U&dib=eyJ2IjoiMSJ9.IGfR4tzkDBNDI6ezDKpVKIdafII18MgP9DI6sv3qNEaP-JGiAyZXKsUaQ6-cUEyRM8ODrEHPr9CTyi03a2LeVABiieCuLk5R6TBIHtnME2vrvNxDrNokWIDMJXuVLSEvBbXc3YUrvBdfv5W95Io9SK3Fz1ykKFlaW1rHBDwvVhKrfyyFub2xQZq6mT4wXjEz90RZ3-YxgOXXYRA_xqxGOJ-GCcHUt8vDdd7ZHww-BRQ.b1yWMJyEniI0F7VUyBBB4TCNcGuw8079qPE_8JkfWV0&dib_tag=se&keywords=crucial%2Bx9%2B1tb&sprefix=crucial%2Bx9%2B1tb%2Caps%2C105&sr=8-1&th=1

(sorry for long link, great price right now)

These are "little gems" -- small and fast.
USB3.1 gen2 -- plug it into one of the USBc ports, and you'll get read speeds around 900MBps.

Erase it to APFS, then install the OS onto it.
Then either use migration assistant to "bring over what you need", OR, start a "fresh setup".

I have one and currently use it to run Sequoia on my 2018 Mini (which still has Mojave on the internal drive!) ...

 

[apostolosdt]

Consider installing Sequoia on external USB SSD drive instead. Leave your internal storage alone.

Good piece of advice! An extra benefit from that approach is that the external macOS can run on any other Mac, provided that it's compatible of course. I use Samsung T7 for such tasks.

[Incidentally, "thank you" to a moderator who pointed out a stylistic error in a previous post of mine in this thread.]

 

[gilby101]

After reading many reports of Sequoia not running smoothly on Intel machines, I thought I might create an extra partition on my internal SSD and boot from that to test it without erasing my Monterey installation. The 512GB SSD has about 100GB free.

I don't know where "many reports" come from. macOS 15 runs very smoothly on my 2019 iMac. But how much RAM do you have?

100 GB free is cutting it a bit fine. Get an external SSD for your testing. (As others have said).

 

[apostolosdt]

I don't know where "many reports" come from. macOS 15 runs very smoothly on my 2019 iMac. But how much RAM do you have? […]

I have Sequoia installed and running on a Mini 2018 (i5, 32 GB RAM) and it works flawlessly; by the way, from an external disk.