diskutil list
	-bash-3.2# diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS YOUSSA                  999.9 GB   disk0s2
/dev/disk1 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                  Apple_HFS Macintosh HD            499.2 GB   disk1s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3
/dev/disk2 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +2.1 GB     disk2
   1:                  Apple_HFS OS X Base System        2.0 GB     disk2s1
/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *2.0 TB     disk3
   1:               Windows_NTFS TOSHIBA EXT             2.0 TB     disk3s1
/dev/disk4 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +5.2 MB     disk4
/dev/disk5 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk5
/dev/disk6 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk6
/dev/disk7 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk7
/dev/disk8 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk8
/dev/disk9 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk9
/dev/disk10 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +6.3 MB     disk10
/dev/disk11 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +2.1 MB     disk11
/dev/disk12 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +1.0 MB     disk12
/dev/disk13 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk13
/dev/disk14 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +524.3 KB   disk14
/dev/disk15 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +1.0 MB     disk15
/dev/disk16 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            untitled               +6.3 MB     disk16
-bash-3.2#
	diskutil info disk0s2
	-bash-3.2# diskutil info disk0s2
   Device Identifier:        disk0s2
   Device Node:              /dev/disk0s2
   Whole:                    No
   Part of Whole:            disk0
   Device / Media Name:      Untitled 2
   Volume Name:              YOUSSA
   Mounted:                  Yes
   Mount Point:              /Volumes/YOUSSA
   File System Personality:  Journaled HFS+
   Type (Bundle):            hfs
   Name (User Visible):      Mac OS Extended (Journaled)
   Journal:                  Journal size 81920 KB at offset 0x1d1c000
   Owners:                   Enabled
   Partition Type:           Apple_HFS
   OS Can Be Installed:      Yes
   Media Type:               Generic
   Protocol:                 SATA
   SMART Status:             Verified
   Volume UUID:              CFFA1447-013B-355A-A5C3-C78E0F88B6F5
   Disk / Partition UUID:    B80D9611-F319-4A23-B083-A1804A631343
   Total Size:               999.9 GB (999860912128 Bytes) (exactly 1952853344 512-Byte-Units)
   Volume Free Space:        999.2 GB (999197233152 Bytes) (exactly 1951557096 512-Byte-Units)
   Device Block Size:        512 Bytes
   Allocation Block Size:    4096 Bytes
   Read-Only Media:          No
   Read-Only Volume:         No
   Device Location:          Internal
   Removable Media:          No
   Solid State:              No
-bash-3.2#
	mkdir -v /Volumes/YOUSSA/Sauvegarde
	diskutil info disk1s2
	-bash-3.2# diskutil info disk1s2
   Device Identifier:        disk1s2
   Device Node:              /dev/disk1s2
   Whole:                    No
   Part of Whole:            disk1
   Device / Media Name:      Macintosh HD
   Volume Name:              Macintosh HD
   Mounted:                  Yes
   Mount Point:              /Volumes/Macintosh HD
   File System Personality:  HFS+
   Type (Bundle):            hfs
   Name (User Visible):      Mac OS Extended
   Owners:                   Enabled
   Partition Type:           Apple_HFS
   OS Can Be Installed:      No
   Recovery Disk:            disk1s3
   Media Type:               Generic
   Protocol:                 USB
   SMART Status:             Not Supported
   Volume UUID:              87297013-3C81-3C1B-9955-961F351E03B3
   Disk / Partition UUID:    2EEE5CB9-ECE5-4AC6-ADE4-2A817E9FCCA2
   Total Size:               499.2 GB (499248103424 Bytes) (exactly 975093952 512-Byte-Units)
   Volume Free Space:        330.7 GB (330696192000 Bytes) (exactly 645891000 512-Byte-Units)
   Device Block Size:        512 Bytes
   Allocation Block Size:    4096 Bytes
   Read-Only Media:          No
   Read-Only Volume:         Yes
   Device Location:          External
   Removable Media:          No
-bash-3.2#
	mkdir /Volumes/YOUSSA/Sauvegarde
	Si si il est branché.Tu ne branches pas le Mac au secteur ?
Et si tu remets le HDD en branchement USB externe => tu arrives à démarrer via ⌘R sur l'OS de secours ?