How does OS X run on two hard drives?

Discussion in 'Mac OS X Lion (10.7)' started by TheMTtakeover, Jul 5, 2012.

  1. TheMTtakeover macrumors 6502


    Aug 3, 2011
    I was thinking of adding a second hard drive to my MM but I've never had a computer with more than one hard drive. How exactly does it work? Can you access both? Can you chose which to boot from? Can you have applications stored on one and then data files on the other? Any information that anyone can provide would be apperciated.
  2. SandboxGeneral Moderator emeritus


    Sep 8, 2010
    One HDD will have OS X on it and the other typically will only be used for file storage, like music and videos.

    You do not want to spread the OS or various applications across both as that will cause problems.

    The system will know which HDD has OS X and will boot from that.
  3. musycsmk macrumors newbie

    Apr 19, 2012
    Los Angeles, CA
    A lot of people including me use the fast SSD Harddrive if your getting one for Booting and Applications. Just normal HDD as Home Storage.
  4. TheMTtakeover thread starter macrumors 6502


    Aug 3, 2011
    How would you go about setting this up?
  5. robgendreau macrumors 68040

    Jul 13, 2008
    Do some searching.

    You have to decide if you want to add internally or externally.

    The second alternative, external, is far easier. Just buy an external, hook it to your Mac with the appropriate cable, run Disk Utility and format it to HFS+ journaled. Then use it for storage, backups, Time Machine, etc. It acts just like a giant version of all those volumes you've seen pop up from .dmg files you're downloaded.

    Internal is tougher; check out to see what you're getting into. But you can, as suggested, add a SSD drive, which speeds performance of many tasks considerably.

    You can also partition the physical drive, internal or external, into one or more volumes. And one of those could be used to hold a clone of your system. That's very helpful if the other drive fails; you then boot up from the clone and keep working. You can also set up a different system on that other hard drive; lots of folks do that with Snow Leopard if it runs on their machine. Then they keep Lion on the other drive. You can choose which to boot into with Startup Disk in Prefs, or by holding down the option key when you start up.

    It's a good idea you have, you just need to let us know what your needs are so we can suggest which of all these opportunities might help you the most. E.g., you might need lots of storage for media, but have another computer. So you don't need a clone. Or the opposite.

  6. TheMTtakeover thread starter macrumors 6502


    Aug 3, 2011
    I know how to add a second internal hard drive, I'm just curious how it shows up in OSX just like another external hard drive?
  7. CyBeRino macrumors 6502a

    Jun 18, 2011
    It shows up just like another internal hard drive, if you install it internally. (Which you would have to sacrifice the superdrive for in a Mac mini btw.)

    Also as for your questions: all of the above. It basically works exactly as you'd expect it to.
  8. TheMTtakeover thread starter macrumors 6502


    Aug 3, 2011
    My mini doesn't have a drive thanks though I understand now.

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