External drive for booting Yosemite

Discussion in 'OS X Yosemite (10.10)' started by steve217, Sep 19, 2014.

  1. steve217, Sep 19, 2014
    Last edited: Sep 20, 2014

    steve217 macrumors regular


    Nov 11, 2011
    I’m trying out Yosemite and I want to make a boot drive from a spare hard drive that I have from an SSD upgrade in a Windows 7 machine.

    I’ve followed these instructions and even these to create the boot media.

    When I set the startup disk to the external drive, the Mac (mini late 2012) boots straight to the internal drive and back into Mavericks.

    When I hold down the option key during boot, the drive appears as a boot option but with a label of ‘windows’. If I select the drive, I get a ‘Missing operating system’ error. I can then hold the power button and the machine will boot to the external drive.

    I’ve successfully installed Yosemite with the ‘Missing operating system’, force power off, dance, but it’s no fun doing that; especially if I want to switch over to Yosemite to play for a bit.

    Any ideas why the external drive is unbootable for OS/X and appears as a ‘Windows’ drive when I hold option during boot? Is there some arcane Windows boot sector from it’s previous life in a Dell?

    Addt’l info:
    External enclosure - Sabrent USB 3.0 3.5”  ([url]http://www.sabrent.com/category/hard-drive-enclosures/EC-S35K[/url])
    Mac Model Name:	Mac mini
      Model Identifier:	Macmini6,1
      Processor Name:	Intel Core i5
      Memory:	4 GB
    External drive 
    USB to ATA/ATAPI Bridge:[INDENT]
      Product ID:	0x0539
      Vendor ID:	0x152d  (JMicron Technology Corp.)
      Version:	 1.00
      Speed:	Up to 5 Gb/sec
      Manufacturer:	JMicron
      Location ID:	0x15100000 / 3
      Current Available (mA):	900
      Current Required (mA):	0
      Capacity:	500.11 GB (500,107,862,016 bytes)
      Removable Media:	Yes
      Detachable Drive:	Yes
      BSD Name:	disk1
      Partition Map Type:	GPT (GUID Partition Table)
      S.M.A.R.T. status:	Not Supported
      Capacity:	209.7 MB (209,715,200 bytes)
      BSD Name:	disk1s1
      Content:	EFI
      Capacity:	499.25 GB (499,248,103,424 bytes)
      Available:	488.04 GB (488,041,316,352 bytes)
      Writable:	Yes
      File System:	Journaled HFS+
      BSD Name:	disk1s2
      Mount Point:	/Volumes/YosemiteDrive
      Content:	Apple_HFS
    Recovery HD:
      Capacity:	650 MB (650,002,432 bytes)
      BSD Name:	disk1s3
      Content:	Apple_Boot[/INDENT]
  2. atvusr, Sep 19, 2014
    Last edited: Sep 20, 2014

    atvusr macrumors 6502


    Apr 5, 2010
    For installing OS X, make sure that your external Drive has a GUID Partition and is formatted with the 'Mac OS Extended (Journaled)' filesystem. It can be done with the Disk Utility in OS X.

    Most external Drives are formatted for Windows with a MBR Partition and FAT32 or exFAT filesystem. This could be a reason why a Windows HDD appears in the Boot-Options and OS X cannot be installed on it.

    If your external Drive has already the GUID/Mac filesystem and the described error still occurs, try to delete the first sectors of the HDD - all data on the Disk are lost after that (make a Backup first).

    Use the Terminal command 'dd'. But CAUTION: this command is a little bit dangerous - if you use the wrong settings, it can overwrite the data on the wrong disk.

    List your Drives in Terminal with: diskutil list

    Unmount the Disk (i.e. disk1): diskutil unmountdisk disk1

    To write 100 MB (zeros) to the first sectors of the external HDD (i.e. disk1):

    dd if=/dev/zero of=/dev/disk1 bs=1024k count=100

    Disconnect the external Drive, start Disk Utility, reconnect the Drive, maybe OS X asks if the Drive should be initialized - yes. Then create the GUID Partition with the 'Mac OS Extended (Journaled)' filesystem again and try to install Yosemite.
  3. steve217 thread starter macrumors regular


    Nov 11, 2011
    Did and done...

    This was promising, but alas, still no joy selecting the external drive as the startup disk; the boot loader still lists the drive as a 'Windows' drive and won't launch Yosemite.

    I suspect the enclosure is flaky so I am going to try another enclosure and drive.
  4. Madd the Sane macrumors 6502a

    Madd the Sane

    Nov 8, 2010
    I would advise against removing the EFI partition on a drive. While it may not be used now, this may change in the future.

    Perhaps the Yosemete installer is looking for a partition with Mavericks already installed?
  5. atvusr macrumors 6502


    Apr 5, 2010
    You could try to reset the PRAM - see Apple's instructions here.
  6. steve217 thread starter macrumors regular


    Nov 11, 2011
    Thanks everybody.

    It looks like it was the enclosure.

    I installed Yosemite on a SAMSUNG D3 Station 2TB external and everything works flawlessly now; I can select Yosemite to boot from the external without a hiccup.

    I'll just use my $30 SABRENT USB 3.0 then for storage as it seems to handle that chore without any problems.
  7. jimihat macrumors newbie

    Oct 17, 2014
    Dorset, UK
    Hi All

    Just reading this, it seems you can boot to Yosemite from external drive with no problem then? so is it possible to use 100% of the internal drive to run Windows 8.1 from?

    I'm thinking of getting a thunderbolt caddy and putting an old SSD in to run OSX, then using th einternal Fusion Drive to run Windows 8.1.

    Being able to do this or not do this will make or break my decision regarding the new 5k iMac.

    Thanks in advance for your thoughts

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