Partition alert message when using Boot Camp Assistant: "The startup disk cannot be partitioned or restored to a single partition." I have a 13" Early-2015 MBP Retina in which I am trying to install Windows 8.1 on. When I went into bootcamp, I received the ever so common error of:


When I went to the newly designed disk utility, it told me I had 2 partitions. Of course, I knew this couldn't be true, so i went into terminal and typed diskutil list and got:

bash-3.2# diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *121.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh SSD           81.0 GB    disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:                  Apple_HFS Data                    39.3 GB    disk0s4
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh SSD          +80.6 GB    disk1
                                 Logical Volume on disk0s2
                                 9839618F-7659-4E0C-BF5C-48B0C94D5E37
                                 Unencrypted


I want to know:


Which partition to delete
How to delete it in a (preferably safe) way that would make my hard
disk "clean" of everything but my main Macintosh HD partition


Thanks!
You have to delete the Data partition. disk1 (Macintosh SSD) is no real partition/disk but a virtual volume residing in disk0s2 but containing your system.


Backup the content of Data
Open Disk Utility
Choose the superior disk and hit "Partition":


Click on the Data partition and hit the - button:


Click Apply

The Data partition will be removed, the Recovery HD moved to the end of the disk and Macintosh SSD will be expanded:

diskutil list #before
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *68.7 GB    disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage System                  51.2 GB    disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:                  Apple_HFS Data                    16.5 GB    disk0s4
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS System                 +50.9 GB    disk1
                                 Logical Volume on disk0s2
                                 4AACDE41-E3A1-444A-A5F6-C1491F46149E
                                 Unencrypted
diskutil list #after
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *68.7 GB    disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage System                  67.9 GB    disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh SSD          +67.5 GB    disk1
                                 Logical Volume on disk0s2
                                 4AACDE41-E3A1-444A-A5F6-C1491F46149E
                                 Unencrypted