Je n'ai pas de doute sur l'identification du disque: c'est bien le sdc.
Voici la sortie utile de fdisk /dev/sdc:
Commande (m pour l'aide) : p
Disque /dev/sdc : 29,8 GiB, 32010928128 octets, 62521344 secteurs
Unités : secteur de 1 × 512 = 512 octets
Taille de secteur (logique / physique) : 512 octets / 512 octets
taille d'E/S (minimale / optimale) : 512 octets / 512 octets
Type d'étiquette de disque : dos
Identifiant de disque : 0xa05fe7fa
Autrement dit aucune partition.
Par contre, voici un (long) extrait de dmesg.
Il s'y trouve la phrase " Add. Sense: Incompatible medium installed" assez mystérieuse.
[ 274.388026] usb 4-2.3: new high-speed USB device number 7 using ehci-pci
[ 274.480937] usb 4-2.3: New USB device found, idVendor=14cd, idProduct=168a
[ 274.480943] usb 4-2.3: New USB device strings: Mfr=1, Product=3, SerialNumber=2
[ 274.480948] usb 4-2.3: Product: USB Mass Storage Device
[ 274.480951] usb 4-2.3: Manufacturer: USB Device
[ 274.480955] usb 4-2.3: SerialNumber: 816820130806
[ 274.481391] usb-storage 4-2.3:1.0: USB Mass Storage device detected
[ 274.481543] scsi9 : usb-storage 4-2.3:1.0
[ 275.480722] scsi 9:0:0:0: Direct-Access USB Mass Storage Device 1.00 PQ: 0 ANSI: 0
[ 275.481187] sd 9:0:0:0: Attached scsi generic sg2 type 0
[ 275.484620] sd 9:0:0:0: [sdc] 62521344 512-byte logical blocks: (32.0 GB/29.8 GiB)
[ 275.485206] sd 9:0:0:0: [sdc] Write Protect is off
[ 275.485211] sd 9:0:0:0: [sdc] Mode Sense: 03 00 00 00
[ 275.485827] sd 9:0:0:0: [sdc] No Caching mode page found
[ 275.485833] sd 9:0:0:0: [sdc] Assuming drive cache: write through
[ 275.491948] sdc: unknown partition table
[ 275.495074] sd 9:0:0:0: [sdc] Attached SCSI removable disk
[ 275.568051] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 275.744040] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 275.920045] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.108032] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.292045] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.468063] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.644051] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.820060] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 276.996030] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 277.172026] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 277.264581] sd 9:0:0:0: [sdc] Unhandled error code
[ 277.264586] sd 9:0:0:0: [sdc]
[ 277.264589] Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK
[ 277.264593] sd 9:0:0:0: [sdc] CDB:
[ 277.264595] Read(10): 28 00 00 00 00 20 00 00 18 00
[ 277.264612] end_request: I/O error, dev sdc, sector 32
[ 277.264615] quiet_error: 8 callbacks suppressed
[ 277.264618] Buffer I/O error on device sdc, logical block 4
[ 277.264622] Buffer I/O error on device sdc, logical block 5
[ 277.264624] Buffer I/O error on device sdc, logical block 6
[ 277.340026] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 277.516037] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 277.692029] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 277.868028] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 278.044038] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 278.150197] sd 9:0:0:0: [sdc]
[ 278.150202] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
[ 278.150206] sd 9:0:0:0: [sdc]
[ 278.150208] Sense Key : Aborted Command [current]
[ 278.150213] sd 9:0:0:0: [sdc]
[ 278.150218] Add. Sense: Incompatible medium installed
[ 278.150221] sd 9:0:0:0: [sdc] CDB:
[ 278.150223] Read(10): 28 00 00 00 00 40 00 00 38 00
[ 278.150238] end_request: I/O error, dev sdc, sector 64
[ 278.150242] Buffer I/O error on device sdc, logical block 8
[ 278.150246] Buffer I/O error on device sdc, logical block 9
[ 278.150248] Buffer I/O error on device sdc, logical block 10
[ 278.150250] Buffer I/O error on device sdc, logical block 11
[ 278.150253] Buffer I/O error on device sdc, logical block 12
[ 278.150254] Buffer I/O error on device sdc, logical block 13
[ 278.150257] Buffer I/O error on device sdc, logical block 14
[ 278.528027] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 278.704043] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 278.880035] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci
[ 279.002824] sdc: unknown partition table
[ 279.100023] usb 4-2.3: reset high-speed USB device number 7 using ehci-pci