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macrumors 68040
Original poster
Jun 5, 2013
Just checking if anyone knows a definitive answer to this - I want to reinstall High Sierra in place (presumably from recovery), without wiping the disk - just a refresh of the Apple system software.

If the disk is already HFS+, will it convert to APFS, or can the terminal prompts to install without conversion be used for an in-place reinstall?



macrumors regular
Feb 21, 2020
In the What we know so far of Ventura, i posted that i like High Sierra more than a modern OS due to is more faster for low processor machines like the Macbook Retina and some user posted a guide to install mojave and install secuurty patches under a HFS+ format. I dont know if the process will work with high sierra but you can test it:

This guides was created by the user JosephAW

Quite simple but may take a day to complete depending on your amount of data and USB port speeds:​
-Obviously backup your data and disconnect your backup drive for safe keeping.​
-Assuming coming from older MacOS like El Capitan or Sierra or High Sierra and your computer supports Mojave or higher. If it doesn’t support Mojave there’s another program called dosdude1 but that’s a little more complicated and found in the other forums here at MR.​
-Set up a new empty external hard drive that is about the same size of your older hard drive or larger, choose Guid: HFS+ In disk utility, use a different name on external drive. Drive doesn't have to be SSD it’ll just be really slow. (Be careful when using disk utility to only choose and erase the new external hard drive and not any other drives.)​
-Download carbon copy cloner from bombich website. (throw them a bone if everything works great.)​
-Clone your old High Sierra internal drive to the destination of the new external drive with safety net off. If it asks you to copying the recovery partition you can try to hit yes. (Depending on your amount of data and whether you’re on USB2 or USB3 this copy could take all night for everything.) [Make sure your external drive doesn’t get too hot from all that data, I was using a sata dock and the drive was very warm so I kept the fan on it.]​
-After copy completes Boot from new drive by rebooting computer and hold option key and select new disk.​
-Desktop and files should look identical to your older drive, you can get info on your old hard drive and the new one and they should be within a gigabytes of each other. (Carbon copy cloner doesn’t copy the trash or some temporary files so that’s why there could be some differences.) If not or if a lot of data is missing reboot and go back and start over again with a copy and make sure it completes without error.​
-Eject old High Sierra disk. That way you’ll know you’re on the correct external hard drive.​
-Download Mojave:​

Download and install current or previous versions of the Mac operating system.​​
(You may need to change clock back to 2019 if certificates are expired on your installer.)​
-Install Mojave from applications folder.​
-It will take a while and reboot many times. (You may hear a long tone from your computer and a funny looking progress bar, don’t panic that’s just the software updating the firmware on your computer that Mojave brings along.)​
-A new introductory screen may appear, answer the questions.​
-Once it’s done you’ll notice that the new hard drive disk is now in APFS format after the desktop appears.​
-Correct the clock to today’s date.​
-Apply all security updates on new Mojave disk until no more updates. (Updates moved back into the system preferences. Or Apple menu/about this Mac/system updates.)​
-The computer may seem unresponsive at times and take a long time to shut down or reboot but that’s the slowness of the APFS, You may see a swirly, just let it continue it’ll finish eventually.​
-Don’t open mail or other apps yet.​
-Run carbon copy cloner from bombich again, if it asks you about a previous task you can delete it.​
-Clone the external Mojave hard drive to the destination of the old High Sierra drive with safety net off.
(Copy shouldn’t take as long because it’s only copying the operating system changes and not your user folders, it might be around 15 GB of differences or less.)​
-After copy completes reboot computer, Hold option key, select your original hard drive.​
-Once you get your desktop, go to system preferences and change the start up disk to your normal hard drive.​
-You can eject the new external disk.​
-Launch all your apps like Mail and let it upgrade your data to the Mojave version.​
-When you feel comfortable that everything came across correctly you can reconnect your back up drive and continue from there on.​
-Mojave will be the last version of macOS you can run that supports older 32 bit apps, I’m still using iDVD in Mojave and it works great.​
-Now you get a few more years out of your computer.​
The reason we had to apply the security updates in Apple‘s APFS file system is because security updates will not install with HFS+.​
Since Apple has discontinued security updates for Mojave you no longer need the APFS file system.​
Other updates like App Store updates and Safari updates will still install under HFS+ if they become available.​
Unfortunately the APFS file system is very slow on older computers with a mechanical hard drive but we know that older computers running HFS+ are still very snappy.​
So if you use a SSD formatted to HFS+ It will result in even faster boot times than Apple’s APFS file system on older hardware.​
(I think I covered everything.)​


macrumors 68040
Original poster
Jun 5, 2013
(I think I covered everything.)​

My question was: if I reinstall High Sierra over an existing HFS+ High Sierra install, will it convert the drive to APFS, or can that be avoided with the terminal commands used to avoid it for a fresh install?

I can't find the answer to that in your response.
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