Rethinking the OS X Installation

Discussion in 'macOS' started by bradl, Feb 7, 2014.

  1. bradl macrumors 68040


    Jun 16, 2008
    Instead of asking the same questions asked many times before, and looking at FAQs, I'm going to post a question on a different take of the OS X installation.

    First, I'm running Lion on my 2012 MacBook Air. So far, no problems, and I'm actually happy with it, except for the fact that if I lose the drive, I also lose the data I have along with it. That's okay, because that is what backups are for.

    But when it comes to reinstalling, or even updating the OS, it still would go back on to the same piece of hardware (meaning, the internal drive). Or does it have to be that way?

    I ask that, because in my professional life as a Linux sysadmin, I'm running a boatload of virtual servers off of Dell servers, which the base OS is VMWare ESXi, which has the option of having the base OS installed onto a USB stick, leaving the internal drives solely for hosting the virtual servers or a datastore.

    That same process could be used on a Mac, could it not? But instead of a USB stick, use a SDHC card? I know that at that time, the 11" MBA came in a 64GB variant, meaning that the complete OS, after being installed, was definitely less than 64GB.

    So my questions are:
    1. How much space is taken up after a vanilla install of Mavericks? Nothing else but the base OS?
    2. If small enough, could it fit on something like a 64GB SDHC card? If so,
    3. how does read/write speeds compare between an SDHC card vs. various SSDs that Macs use?
    4. Finally, If the OS is installed on an SDHC card, if the internal drive isn't erased, that should give one the option of dual booting, should it not?

    If so, this would not only give me a 64GB to the 256GB internal drive I have by separating the OS off of the internal drive, plus also give me the ability to try out Mavericks without doing a full blown upgrade with no downgrade path.


  2. Nermal Moderator


    Staff Member

    Dec 7, 2002
    New Zealand
    1. I'm not sure of the exact figure but it's definitely less than 64 GB, so...
    2. Yes.
    3. Don't know (it'll surely be slower but I don't know the specifics).
    4. Yes.

    I'm assuming that a Mac can boot from SD; I've never actually tried that.
  3. mfram macrumors 65816

    Jan 23, 2010
    San Diego, CA USA
    Yep, out of the box is about 10GB. You can fit it on an SDCard no problem. But most SDCards will be a lot slower than the internal SSD.
  4. Dark Dragoon macrumors 6502a

    Dark Dragoon

    Jul 28, 2006
    You are probably looking at performance of around 400-500MB/s Read and Write (sequential) on the MBA's internal SSD though of-course this varies. For random it is a lot lower.

    For a good SD card you are probably going to see it max out at 60MB/s Write, 90MB/s Read (sequential) but if you get a cheaper card it will more likely be around 20MB/s Write, 50MB/s Read (sequential) if you are lucky. However it appears that the card reader in the 2012 MBA is capped at around 40MB/s anyway.

    So you will probably see about 1/10th the performance with an SD card at best, for random reads and writes it may be a lot worse.

    The main difference here is that with VMWare ESXi the host doesn't really need to read and write much data to the drive it is installed on, instead all the reads and writes are hitting the fast internal drives where the vm's are stored. Versus here where all the reads and writes would be hitting the slow SD card.

    However there shouldn't really be any reason why you couldn't install Mavericks onto an SD card (or a much faster USB3 external HDD/SSD), the Mavericks installer .app will let you choose which drive to install the OS onto (or you can create a bootable USB installer). You can select what drive to boot from by holding down alt/option at boot.

    Alternatively you could clone your internal drive to an external as a bootable backup, then update to Mavericks on the internal. If you don't like it you can clone back from the backup.
  5. bradl thread starter macrumors 68040


    Jun 16, 2008
    Definitely good ideas here. The thing I was thinking of was if I didn't have to carry around something external and didn't have to crack open the Mac and doing a rip/replace on the SSD that is installed, that would be an easier way to add space for an OS-only disk without spending the couple hundred dollars it would be to buy a larger SSD to go in the Mac.

    In short, drop in a card to the SD slot, so all would remain internal, and off you go.

    The only concern I would have would have been the I/O speeds of the SD card, which would definitely be slower, but I didn't know how much slower.

    That was what I was thinking. I just didn't know how much of it was.

    I'll do a bit more research into it and see what I can see.

  6. SlCKB0Y, Mar 15, 2014
    Last edited: Mar 15, 2014

    SlCKB0Y macrumors 68040


    Feb 25, 2012
    Sydney, Australia
    OS X run from a SD slot will almost be unusably slow.

    ESXi on your work servers is usable from SD because it is probably running in RAM and it isn't really doing any writes to SD.

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