What causes this HDD sector damage pattern?

Out of curiosity, I ran GNU ddrescue on a Seagate ST1000LM024 HN-M101MBB hard drive with known bad sectors, and then I visualized the ddrescue mapfile with ddrescueview.

When I zoomed in, this interesting patte appeared:

The green gaps (contiguous good sectors) are often 2440 logical sectors (1249280 bytes) large, and the red sections (bad and probably physically damaged sectors) are almost always 1 physical sector (4 logical sectors, 4096 bytes) large.

Keeping this patte in mind, I did a calculation to estimate how many sectors would be on the track. The hard drive spins at 5400 rotations per minute, the sustained read rate at that part of the drive is about 109 mebibytes per second (I tested this on a drive of the same model with no bad sectors), one track goes around 360 degrees, and a logical sector is 512 bytes.

((109MiB/s / 5400rpm * 360 degrees) / 512 bytes) = 2480

The estimation shows that there are about 2480 logical sectors in the affected track. The patte happens every 2444 logical sectors.

This suggests that the physical damage looks like a very thin strip heading inwards practically tangent to the circle of the platter. The thin strip fits in an arc less than 0.001639°. This damage, whatever it is, appears to be a microscopic gash.

There are other characteristics of the patte that I can't quite make sense of.

• The bad sectors only exist in the first ¹/₆ of the drive, the outer edges, with no clear patte of where the bands of pattes appear.
• The pattes don't appear to be one long gash; they're more like a dotted/dashed line ("┋"):

Why would damage appear like this? What could create such an orderly damage patte?

S.M.A.R.T.

# smartctl -a /dev/sdf
smartctl 6.4 2014-10-07 r4002 [x86_64-linux-4.3.0-0.bpo.1-amd64] (local build)
Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org
=== START OF INFORMATION SECTION ===
Model Family: Seagate Momentus SpinPoint M8 (AF)
Device Model: ST1000LM024 HN-M101MBB
Serial Number: S314J90G121745
LU WWN Device Id: 5 0004cf 20f07d081
Firmware Version: 2BA30003
User Capacity: 1,000,204,886,016 bytes [1.00 TB]
Sector Sizes: 512 bytes logical, 4096 bytes physical
Rotation Rate: 5400 rpm
Form Factor: 2.5 inches
Device is: In smartctl database [for details use: -P show]
ATA Version is: ATA8-ACS T13/1699-D revision 6
SATA Version is: SATA 3.0, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is: Sat Mar 19 10:02:27 2016 CDT
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: (0x00) Offline data collection activity was never started. Auto Offline Data Collection: Disabled.
Self-test execution status: ( 121) The previous self-test completed having the read element of the test failed.
Total time to complete Offline
data collection: (12480) seconds.
Offline data collection
capabilities: (0x5b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. No 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: ( 208) minutes.
SCT capabilities: (0x003f) SCT Status supported. SCT Error Recovery Control 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 100 100 051 Pre-fail Always - 118722 2 Throughput_Performance 0x0026 252 252 000 Old_age Always - 0 3 Spin_Up_Time 0x0023 092 092 025 Pre-fail Always - 2494 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 96 5 Reallocated_Sector_Ct 0x0033 252 252 010 Pre-fail Always - 0 7 Seek_Error_Rate 0x002e 252 252 051 Old_age Always - 0 8 Seek_Time_Performance 0x0024 252 252 015 Old_age Offline - 0 9 Power_On_Hours 0x0032 100 100 000 Old_age Always - 4188 10 Spin_Retry_Count 0x0032 252 252 051 Old_age Always - 0 11 Calibration_Retry_Count 0x0032 100 100 000 Old_age Always - 21 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 102 13 Read_Soft_Error_Rate 0x003a 100 100 000 Old_age Always - 0
181 Program_Fail_Cnt_Total 0x0022 100 100 000 Old_age Always - 655675
191 G-Sense_Error_Rate 0x0022 100 100 000 Old_age Always - 56
192 Power-Off_Retract_Count 0x0022 100 100 000 Old_age Always - 25
193 Load_Cycle_Count 0x0032 089 089 000 Old_age Always - 111986
194 Temperature_Celsius 0x0002 058 050 000 Old_age Always - 42 (Min/Max 14/50)
195 Hardware_ECC_Recovered 0x003a 100 100 000 Old_age Always - 0
196 Reallocated_Event_Count 0x0032 252 252 000 Old_age Always - 0
197 Current_Pending_Sector 0x0032 037 037 000 Old_age Always - 10437
198 Offline_Uncorrectable 0x0030 252 252 000 Old_age Offline - 0
199 UDMA_CRC_Error_Count 0x0036 200 200 000 Old_age Always - 0
200 Multi_Zone_Error_Rate 0x002a 100 100 000 Old_age Always - 3688
240 Head_Flying_Hours 0x0032 100 100 000 Old_age Always - 4186
241 Total_LBAs_Written 0x0032 097 094 000 Old_age Always - 4770327
242 Total_LBAs_Read 0x0032 096 094 000 Old_age Always - 5931956
254 Free_Fall_Sensor 0x0032 252 252 000 Old_age Always - 0
SMART Error Log Version: 1
Waing: ATA error count 13458 inconsistent with error log pointer 4
ATA Error Count: 13458 (device log contains only the most recent five errors) CR = Command Register [HEX] FR = Features Register [HEX] SC = Sector Count Register [HEX] SN = Sector Number Register [HEX] CL = Cylinder Low Register [HEX] CH = Cylinder High Register [HEX] DH = Device/Head Register [HEX] DC = Device Command Register [HEX] ER = Error register [HEX] ST = Status register [HEX]
Powered_Up_Time is measured from power on, and printed as
DDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes,
SS=sec, and sss=millisec. It "wraps" after 49.710 days.
Error 13458 occurred at disk power-on lifetime: 4188 hours (174 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 08 28 ec cb e2 Error: UNC 8 sectors at LBA = 0x02cbec28 = 46918696 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 08 28 ec cb e2 08 00:02:49.684 READ DMA b0 d5 01 00 4f c2 00 08 00:02:49.684 SMART READ LOG ef 10 02 00 00 00 a0 08 00:02:49.684 SET FEATURES [Enable SATA feature] 27 00 00 00 00 00 e0 08 00:02:49.684 READ NATIVE MAX ADDRESS EXT [OBS-ACS-3] ec 00 00 00 00 00 a0 08 00:02:49.684 IDENTIFY DEVICE
Error 13457 occurred at disk power-on lifetime: 4188 hours (174 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 08 28 ec cb e2 Error: UNC 8 sectors at LBA = 0x02cbec28 = 46918696 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 08 28 ec cb e2 08 00:02:49.681 READ DMA b0 da 00 00 4f c2 00 08 00:02:49.681 SMART RETURN STATUS ef 10 02 00 00 00 a0 08 00:02:49.681 SET FEATURES [Enable SATA feature] 27 00 00 00 00 00 e0 08 00:02:49.681 READ NATIVE MAX ADDRESS EXT [OBS-ACS-3] ec 00 00 00 00 00 a0 08 00:02:49.681 IDENTIFY DEVICE
Error 13456 occurred at disk power-on lifetime: 4188 hours (174 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 08 28 ec cb e2 Error: UNC 8 sectors at LBA = 0x02cbec28 = 46918696 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 08 28 ec cb e2 08 00:02:49.677 READ DMA b0 d1 01 01 4f c2 00 08 00:02:49.677 SMART READ ATTRIBUTE THRESHOLDS [OBS-4] ef 10 02 00 00 00 a0 08 00:02:49.677 SET FEATURES [Enable SATA feature] 27 00 00 00 00 00 e0 08 00:02:49.677 READ NATIVE MAX ADDRESS EXT [OBS-ACS-3] ec 00 00 00 00 00 a0 08 00:02:49.677 IDENTIFY DEVICE
Error 13455 occurred at disk power-on lifetime: 4188 hours (174 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 08 28 ec cb e2 Error: UNC 8 sectors at LBA = 0x02cbec28 = 46918696 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 08 28 ec cb e2 08 00:02:49.674 READ DMA b0 d0 01 00 4f c2 00 08 00:02:49.674 SMART READ DATA ef 10 02 00 00 00 a0 08 00:02:49.674 SET FEATURES [Enable SATA feature] 27 00 00 00 00 00 e0 08 00:02:49.674 READ NATIVE MAX ADDRESS EXT [OBS-ACS-3] ec 00 00 00 00 00 a0 08 00:02:49.674 IDENTIFY DEVICE
Error 13454 occurred at disk power-on lifetime: 4188 hours (174 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 08 28 ec cb e2 Error: UNC 8 sectors at LBA = 0x02cbec28 = 46918696 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 08 28 ec cb e2 08 00:02:49.670 READ DMA ec 00 01 00 00 00 00 08 00:02:49.670 IDENTIFY DEVICE ef 10 02 00 00 00 a0 08 00:02:49.670 SET FEATURES [Enable SATA feature] 27 00 00 00 00 00 e0 08 00:02:49.670 READ NATIVE MAX ADDRESS EXT [OBS-ACS-3] ec 00 00 00 00 00 a0 08 00:02:49.670 IDENTIFY DEVICE
SMART Self-test log structure revision number 1
Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error
# 1 Short offline Completed: read failure 90% 4101 933752
# 2 Short offline Completed: read failure 90% 4101 933752
# 3 Short offline Completed: read failure 90% 4101 1417744
# 4 Short offline Completed without error 00% 3607 -
# 5 Short offline Completed without error 00% 3002 -
# 6 Short offline Completed without error 00% 2338 -
# 7 Short offline Completed without error 00% 1044 -
# 8 Short offline Completed without error 00% 334 -
# 9 Short offline Completed without error 00% 0 -
SMART Selective self-test log data structure revision number 0
Note: revision number not 1 implies that no selective self-test has ever been run SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS 1 0 0 Completed_read_failure [90% left] (0-65535) 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.

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