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I have Samsung 840 Pro SSD which is working for a while for a MySQL database server. I felt it has become slow recently, so I tested it with smartctl:

#smartctl -a  /dev/sda
smartctl 6.4 2014-10-07 r4002 [x86_64-linux-3.16.0-4-amd64] (local build)
Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Model Family:     Samsung based SSDs
Device Model:     Samsung SSD 840 PRO Series
Serial Number:    S1AXNSAF210103T
LU WWN Device Id: 5 002538 5a01db814
Firmware Version: DXM05B0Q
User Capacity:    512,110,190,592 bytes [512 GB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ACS-2, ATA8-ACS T13/1699-D revision 4c
SATA Version is:  SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Fri Mar 27 00:25:00 2020 EDT
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:      (   0) The previous self-test routine completed
                    without error or no self-test has ever 
                    been run.
Total time to complete Offline 
data collection:        (53956) seconds.
Offline data collection
capabilities:            (0x53) SMART execute Offline immediate.
                    Auto Offline data collection on/off support.
                    Suspend Offline collection upon new
                    command.
                    No 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:    (  35) minutes.
SCT capabilities:          (0x003d) SCT Status supported.
                    SCT Error Recovery Control supported.
                    SCT Feature Control supported.
                    SCT Data Table supported.

SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   092   092   000    Old_age   Always       -       35740
 12 Power_Cycle_Count       0x0032   099   099   000    Old_age   Always       -       18
177 Wear_Leveling_Count     0x0013   085   085   000    Pre-fail  Always       -       522
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   100   100   010    Pre-fail  Always       -       0
181 Program_Fail_Cnt_Total  0x0032   100   100   010    Old_age   Always       -       0
182 Erase_Fail_Count_Total  0x0032   100   100   010    Old_age   Always       -       0
183 Runtime_Bad_Block       0x0013   100   100   010    Pre-fail  Always       -       0
187 Uncorrectable_Error_Cnt 0x0032   100   100   000    Old_age   Always       -       0
190 Airflow_Temperature_Cel 0x0032   073   057   000    Old_age   Always       -       27
195 ECC_Error_Rate          0x001a   200   200   000    Old_age   Always       -       0
199 CRC_Error_Count         0x003e   100   100   000    Old_age   Always       -       0
235 POR_Recovery_Count      0x0012   099   099   000    Old_age   Always       -       12
241 Total_LBAs_Written      0x0032   099   099   000    Old_age   Always       -       25524754306

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  Short offline       Completed without error       00%     35740         -

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
  255        0    65535  Read_scanning was never started
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.

The strange thing is that Wear_Leveling_Count is 522. But I've read that it should start at 100 and gradually get closer to 0 as the disk wears out.

So I'm wondering how to interpret this number? And whether there is the more reliable way to check the disk's health?

Milkyway
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    You might want to 1st Update your versioin of smartctl "2019-12-30: We released ​version 7.1 of Smartmontools." https://www.smartmontools.org/ Here is the documentation in case you have not seen it: https://www.smartmontools.org/wiki/TocDoc Hope this can help. – vssher Mar 27 '20 at 05:24
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    The [warranty of the 840](https://www.samsung.com/semiconductor/minisite/ssd/support/warranty/) is for 3 years and the PRO version had 73 TB TBW. You have 4 years power on and over 10 TBW. You may consider replacing the disk, or otherwise monitor it constantly for more serious indicators of failures like reallocated sectors. It's not fun to recover a database from files with corrupted blocks, so replacing the disk is probably the cheapest choice. – Nemo Mar 08 '21 at 06:41

1 Answers1

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Each SMART attribute has two values: A raw value and a normalized value (aka current value). In the output of smartctl -a, the normalized value is reported under the column with heading VALUE, while the raw value is under the heading RAW_VALUE (see the man page).

For the Wear_Leveling_Count attribute (ID#177), the normalized value estimates the remaining life in percentage, which in your output is 085 or 85%. (The raw value of 522 is less useful to the user, as it is a drive-specific number giving the total count of program erase cycles, averaged per block.)

So your drive had an estimated 85% remaining life.

See this thread for more. Unfortunately a large number of threads fail to correctly distinguish and interpret these two fields (normalized and raw), causing great confusion!

GDGP
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