The difference of Apple+option+R & Apple+R

[blackxacto]

17,1 iMac 10.12.6 w Fusion Drive

Tonite I wanted to reinstall Sierra 10.12.6. So I chose to hold Apple+Option+R, then rebooted. The installer window then asked me to CONTINUE to install High Sierra. I stopped.

I rebooted, holding Apple+R, and was asked to install Sierra. I stopped to ask the forum a question:

Why would I be asked to install High Sierra on a Fusion Drive?
What is the difference in the two key combinations?

Normally in the past, I thought either key combo would allow me to install the latest system, for my iMac. Has that changed?

 

[prisstratton]

Please read this page, it should answer your questions:

https://support.apple.com/en-ca/HT204904

 

[blackxacto]

“Option-Command-R. Upgrade to the latest macOS that is compatible with your Mac.”

Why I posted to the forum is because this key combo, gave me the High Sierra download, which ain’t compatible with my fusion drive iMac?

 

[prisstratton]

The title of your thread asked about the difference between the two options, the page I listed showed that difference.

Your system with a fusion drive can install High Sierra, it would just use the existing HFS+ format as opposed to the new APFS. Full APFS support for fusion drives will come in a future release.

Your stated that you wanted to reinstall Sierra, so why are you worrying about High Sierra.

 

[blackxacto]

Had no idea HS could be safely installed on fusion drives. Where did you see Apple saying this was possible?

 

[prisstratton]

I have not seen any specific report from Apple that explicitly states that.

However, people are reporting that it does install on fusion drives, but the HFS+ format is maintained, please see here:

https://forums.macrumors.com/threads/fusion-drive-seems-slow-after-high-sierra-update.2073204/

Proceed at your own risk.

Personally, I would not perform this upgrade until your fusion drive is fully supported, why go through two upgrade processes.

And…..back to your original statement.

“Tonite I wanted to reinstall Sierra 10.12.6.”

“I rebooted, holding Apple+R, and was asked to install Sierra.”

I would suggest you proceed as you originally planned.

More info regarding fusion drives and High Sierra, here:

https://www.macrumors.com/2017/09/18/apple-files-system-no-fusion-drive-support/
https://www.macrumors.com/2017/09/25/apfs-fusion-drive-high-sierra-update/

Hope it helps.

Good luck.