Slow boot with external Mojave

  1. 8 months ago

    Since the installation of Mojave my iMac (21" retina 2017) has a very slow boot from the external USB SSD Mojave OS.
    I have an internal drive 5400rpm with El Capitán and BootCamp, by disconnecting the external SSD it boots fast from both El Capitán and Windows (as fast as this disk allows) but once I connect the external SSD drive all boots are slow (may be 5 minutes until working).
    It takes just a lot to show the Startup manager (after pressing option while booting) and then more to show the Apple logo.

    With High Sierra external SSD was ver fast, I have tried:

    • With a second USB SSD with Mojave (prerelease OS): same result.
    • Performed diagnostics, Disk utility, etc, all is fine.
    • Formatted all drives and reinstalled anything in both drives, internal with Capitán and BootCamp and external with Mojave: same result.

    I have checked USB drive speed and seems normal for an USB SSD. Awaking from sleep takes more than normal but I have not noticed any lag in applications once it is working.

    I'm not 100% sure Mojave start it but I already noticed something abnormal with the testing Mojave SSD.

  2. Jason P

    2 Oct 2018 Xojo Inc Texas

    Norm has had similar issues with Mojave on an external drive. Two of real note - 1 repeated persistent kernel panics after about 2 hours. And when Mojave on the external puts the machine in sleep mode and is then awoken the externals are not powered back up meaning he then has to power the machine off to get it to come back to life.

  3. Thanks Jason, will make a search about USB issues. May be I have to switch Thunderbolt but price vs. speed difference is not attractive.

  4. Hate to break it to you, but a USB-C connected external drive is just as slow.

  5. Tim J

    2 Oct 2018 Pre-Release Testers, Xojo Pro Dehydrating in AZ

    I boot both my rMBP and my Trash Can from an external USB-3 Mojave volume in a Cooler Master dock and it's as fast as any other OS version I boot from that same dock.

    Are you updating the startup volume with the drive connected before you reboot?

  6. Greg, It was very fast in previous OS versions, at least enough for me, probably they are better options but this was fine without breaking warranty and installing SSD internally. Now I'm tempted to open it but have read some issues with fans.

    Tim, not sure to understand you: all volumes are connected, I select external as boot drive in Preferences and reboot.

  7. Jean-Yves P

    3 Oct 2018 Pre-Release Testers, Xojo Pro Europe (France, Besançon)

    it would certainly be better to have the ssd internal and the 5400rpm outside of the imac ...

  8. 7 months ago

    Tim J

    4 Oct 2018 Pre-Release Testers, Xojo Pro Dehydrating in AZ

    @AlejandroFresno ;Meyer Tim, not sure to understand you: all volumes are connected, I select external as boot drive in Preferences and reboot.

    I've witnessed slow boots when I disconnected the external drive with it set as the startup volume. When I next reconnected it and rebooted the Mac, it was thoroughly confused as to which drive to boot since I'd never set the internal drive as the startup volume. Reassigning the external drive as the startup volume returned the normal boot time.

  9. Thanks Tim for the info, it's not the case as I have kept it connected and rebooted several times making sure it was the boot drive at preferences.

  10. Just an update in case someone is interested:

    It seems that USB is not 100% compatible with APFS ( ), therefore I have reformatted drive to HFS+ and reinstalled Mojave from TimeMachine backup. Now it is running fine again.

    I have read that Mojave should run in APFS and most probably at any time later I will be forced to change again but hope Apple will solve this bug until then.

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