Last login: Mon Nov 2 19:22:01 on ttys000
iMac:~ olivierlafforgue$ diskutil unmount /dev/disk4
disk4 was already unmounted or it has a partitioning scheme so use "diskutil unmountDisk" instead
iMac:~ olivierlafforgue$ diskutil unmount /dev/disk4s2
Volume Installer on disk4s2 unmounted
iMac:~ olivierlafforgue$ 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 HD 121.0 GB disk0s2
3: Apple_Boot Boot OS X 134.2 MB disk0s3
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_CoreStorage Macintosh HD 999.3 GB disk1s2
3: Apple_Boot Recovery HD 650.1 MB disk1s3
/dev/disk2 (internal, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS ImacDD +1.1 TB disk2
Logical Volume on disk0s2, disk1s2
E29BC4EE-F172-43AB-A43A-9AD6712847CF
Unencrypted Fusion Drive
/dev/disk4 (disk image):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_partition_scheme +102.4 MB disk4
1: Apple_partition_map 32.3 KB disk4s1
2: Apple_HFS Installer 102.4 MB disk4s2
iMac:~ olivierlafforgue$