OS X Mavericks: If you can’t install OS X on an external disk
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You may need to repartition the disk because it may not have the partition scheme required. You can install OS X only on drives with the GUID Partition Table scheme.
To check the external disk’s partition scheme:
- Open Disk Utility, then select the disk in the list on the left.
- Choose File > Get Info, then look for the Partition Map Scheme. If the disk’s scheme isn’t GUID Partition Table, repartition the disk.
If you don’t see the Partition Map Scheme, you may have selected the volume instead of the disk. (Disks are flush left, with their volumes indented below them.)
If you need to repartition your disk, first back up any important data.
Partition a disk
After the disk is partitioned, you can install OS X, then restore any data you backed up.
Last Modified: Oct 20, 2015