Using two different boot disks - things to know?

Discussion in 'macOS' started by smithrh, Feb 5, 2017.

  1. smithrh macrumors 68020


    Feb 28, 2009
    Sadly, I killed my 2012 MBP the other day (entirely my fault and almost certainly fatal), and I've had to rush to get another MBP up and running.

    Luckily, with the old design I was able to remove the SSD and it's in good working order. The replacement MBP is one of the 2016 models, so only USB-C/TB3 ports, but I've been able to boot to the old SSD without too many issues after running around and getting a variety of dongles... (still looking for a USB-C to SATA cable, they do exist but not stocked in stores yet).

    I am very tempted to keep two boot disks - the internal SSD and this external SSD. Some of the dreck that I've accumulated over the years can be left there, while I keep the new MBP fairly pristine. I am also sadly having some issues with the new MBP so it may be headed back (that's for another thread).

    What are the technical impacts of doing this? I already see that licensing is impacted, as Parallels is asking for a key even though it's fully licensed. I would guess that some apps write files/preferences and such directly to the internal drive.

    (as a side note I've run into install issues when there's only one boot drive, and it's external)

    Anything I should be aware of that might bite me sooner or later?
  2. FreakinEurekan macrumors 68040


    Sep 8, 2011
    Eureka Springs, Arkansas
    You've covered the most common issue, licensing. Parallels, Office, Adobe, etc will treat the two disks as separate computers. Mac App Store apps allow multiple installs so no issue with anything from the App Store. But, iTunes will treat each disk as two of your five allowed "Computers" if both are authorized for content.

    It's really not much different from running a 2nd OS in a VM, other than of course they're not concurrent. Cloud services (iCloud, DropBox, IMAP, etc) will treat the internal & external as two different "computers".

    When I've done beta testing of OS X / macOS versions, this is how I do it. The one I'm testing is booted from an external disk, then I go back to the internal for normal use.
  3. smithrh thread starter macrumors 68020


    Feb 28, 2009
    Thanks for the input - I really should file a bug report on the installation issues when the upgrading drive is external, the problems happen every time. I have an iMac that I boot externally with an SSD on a SATA sled via Thunderbolt, it works great in every way except for the first reboot during the software installation - it just doesn't boot from it, it continues to look for a bootable internal drive and I'll eventually get the flashing question mark.

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