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Question: High Sierra extremely slow startup

4 minutes from internal drive (hdd), 13 minutes from cloned backup on external drive (cloned with Super Duper 3.1.1, the version that's supposed to be working with the APFS format).

Mac mini (Late 2014), macOS High Sierra (10.13.2), HDD drive

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No. Unfortunately, unlike CoreStorage volumes there is no revert with APFS.


Your only option is to back up your system, boot from a High Sierra USB thumb drive, clone or Time Machine back up drive, launch High Sierra's Disk Utility, change the View to Show All Devices, Erase the APFS Container changing the format to Mac OS X Extended (Journaled), reinstall High Sierra and restore your user accounts/data.


It is important to note you must use High Sierra's Disk Utility to erase the APFS Container and reformat.

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Dec 11, 2017 12:38 PM in response to JimmyCMPIT In response to JimmyCMPIT

I just got home for my lunch break. I had started the boot-up from the external drive when I left for work, and after 6 hours it was still showing the Apple logo with an incomplete progress bar. This is ridiculous. How do get back to Sierra?

Dec 11, 2017 12:38 PM

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Dec 12, 2017 5:29 AM in response to Tyler the Wolf In response to Tyler the Wolf

Shut down

Disconnect all external devices all but video, mouse, keyboard

reset the smc

https://support.apple.com/en-us/HT201295

repeat 2/3 times


reset the NVRAM

How to reset NVRAM on your Mac - Apple Support

repeat 2/3 times

then boot into safe mode

https://support.apple.com/en-us/HT201262


then reboot normally with devices disconnected.


if that fails check the drive with disk recovery

About macOS Recovery - Apple Support


if you need to revert back to a previous OS you can either install from a bootable image, or use recovery mode to restore the OS your computer originally shipped with. a "downgrade" will require a blank drive or partition, you can not install over a newer OS image unless you wipe the drive entirely which will eradicate all the data.

you can use Time Machine

How to use Time Machine to back up or restore your Mac - Apple Support

then Apples built in migration assistant to restore your files.

How to move your content to a new Mac - Apple Support

Dec 12, 2017 5:29 AM

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Dec 12, 2017 6:24 AM in response to Tyler the Wolf In response to Tyler the Wolf

Are both your internal HDD and your external drive formatted as APFS? If so, this would explain the slow start up as APFS isn't ready for HDD or Fusion Drives at this time. Only SSDs should be used with APFS.

Dec 12, 2017 6:24 AM

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Dec 14, 2017 6:19 AM in response to keg55 In response to keg55

Major Bummer. I saw the advise that, in order to enjoy the speed improvements of High Sierra all drives must be APFS. So I converted all my drives to that format. I understand there is no way to reverse that. Or is there?

Dec 14, 2017 6:19 AM

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Dec 12, 2017 6:46 AM in response to Tyler the Wolf In response to Tyler the Wolf

No. Unfortunately, unlike CoreStorage volumes there is no revert with APFS.


Your only option is to back up your system, boot from a High Sierra USB thumb drive, clone or Time Machine back up drive, launch High Sierra's Disk Utility, change the View to Show All Devices, Erase the APFS Container changing the format to Mac OS X Extended (Journaled), reinstall High Sierra and restore your user accounts/data.


It is important to note you must use High Sierra's Disk Utility to erase the APFS Container and reformat.

Dec 12, 2017 6:46 AM

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Dec 14, 2017 6:25 AM in response to keg55 In response to keg55

Thanks Keg55. This was very helpful. I reset all my external drives and the internal drive and reloaded them from backups. The startup time from the internal drive is down to between 1 and 1.5 minutes, depending on how many peripherals are attached. Not blazing fast, but this particular computer never started up very fast, with any OS. I can live with that.

The important part for me is that it will now startup reliably from external drives. It didn't always do that before. Now I am comfortable working with this computer again because I know I can start it up from a backup if needed.

Dec 14, 2017 6:25 AM

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Question: High Sierra extremely slow startup