Micron_5300_MTFDDAK480TDS

Just seen an interesting fact on a hard drive with a current Power_On_Hours value of 65966. I launched an extended offline test (using -t long) and the LifeTime? (hours) column does not show the real Power_On_Hours value:

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Green
Device Model:     WDC WD20EARX-00PASB0
Serial Number:    obfuscated
LU WWN Device Id: 5 0014ee 25c9427f5
Firmware Version: 51.0AB51
User Capacity:    2,000,398,934,016 bytes [2.00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ATA8-ACS (minor revision not indicated)
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 3.0 Gb/s)
Local Time is:    Thu Dec 31 15:56:48 2020 CET
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x82)	Offline data collection activity
					was completed without error.
					Auto Offline Data Collection: Enabled.
Self-test execution status:      (   0)	The previous self-test routine completed
					without error or no self-test has ever 
					been run.
Total time to complete Offline 
data collection: 		(38400) seconds.
Offline data collection
capabilities: 			 (0x7b) SMART execute Offline immediate.
					Auto Offline data collection on/off support.
					Suspend Offline collection upon new
					command.
					Offline surface scan supported.
					Self-test supported.
					Conveyance Self-test supported.
					Selective Self-test supported.
SMART capabilities:            (0x0003)	Saves SMART data before entering
					power-saving mode.
					Supports SMART auto save timer.
Error logging capability:        (0x01)	Error logging supported.
					General Purpose Logging supported.
Short self-test routine 
recommended polling time: 	 (   2) minutes.
Extended self-test routine
recommended polling time: 	 ( 370) minutes.
Conveyance self-test routine
recommended polling time: 	 (   5) minutes.
SCT capabilities: 	       (0x3035)	SCT Status supported.
					SCT Feature Control supported.
					SCT Data Table supported.

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   173   167   021    Pre-fail  Always       -       6341
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       161
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   010   010   000    Old_age   Always       -       65966
 10 Spin_Retry_Count        0x0032   100   100   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   100   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       161
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       40
193 Load_Cycle_Count        0x0032   153   153   000    Old_age   Always       -       142788
194 Temperature_Celsius     0x0022   128   110   000    Old_age   Always       -       22
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       0

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%       429         -
# 2  Extended offline    Completed without error       00%       220         -
# 3  Extended offline    Completed without error       00%     63835         -
# 4  Extended offline    Completed without error       00%     21182         -
# 5  Extended offline    Completed without error       00%       971         -
# 6  Short offline       Completed without error       00%       836         -

SMART Selective self-test log data structure revision number 1
 SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

It seems that the maximum Power_On_Hours value is 65535 (interestingly the same value as the maximum network port range). All values above that are shown as difference LifeTime? (hours).

Is this a bug? Is this intended?

PS I Used smartctl 6.6 for this.

USB bridge 0x125f:0xa21a is ADATA HV610 and works with -d sat

Probably just add |21 to existing expression for ADATA in drivedb