Cannot partition hard drive: Cannot unmount error

Question

I was trying to create a new partition on my macbook by booting through Recovery USB using the disk Utility. But I am unable to create a partition since it throws a "Cannot unmount disk" error. I tried to manually unmount the drive but it doesn't work.

Answer 1

Try Erasing the the existing partition first. If the drive has been claimed by CoreStorage, you won't be allowed to change the partitions until it's clean.