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Hard Drive Integrator

SSD Currently unreadable (pending) sectors

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Hi,
We have several i7-6700TE computer systems running CentOS 7.4. We are putting out Transcend 420K 512GB SSD under a read write SSD load. Sometimes we get smartd warnings on systems running our tests. I would like to know What would cause "524288 Currently unreadable (pending) sectors" to show in the SMART logs. This number is always the same:
 
zgrep unreadable /var/log/messages*
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:22:44 node0 smartd[1094]: Device: /dev/sda [SAT], 524288 Currently unreadable (pending) sectors
/var/log/messages.3.gz:Jan 20 01:52:36 node0 smartd[1094]: Device: /dev/sda [SAT], No more Currently unreadable (pending) sectors, warning condition reset after 1 email
smartctl -B +ssd420k.h -a /dev/sda
smartctl 6.2 2017-02-27 r4394 [x86_64-linux-3.10.0-693.2.2.el7.x86_64] (local build)
Copyright (C) 2002-13, Bruce Allen, Christian Franke, www.smartmontools.org
 
=== START OF INFORMATION SECTION ===
Model Family:     SiliconMotion based SSDs
Device Model:     TS512GSSD420K
Serial Number:    D951420059
Firmware Version: O1225G
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 (minor revision not indicated)
SATA Version is:  SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Wed Jan 24 13:50:05 2018 EST
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:                (    0) seconds.
Offline data collection
capabilities:                    (0x71) SMART execute Offline immediate.
                                        No Auto Offline data collection support.
                                        Suspend Offline collection upon new
                                        command.
                                        No Offline surface scan supported.
                                        Self-test supported.
                                        Conveyance Self-test supported.
                                        Selective Self-test supported.
SMART capabilities:            (0x0002) Does not save 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:        (   1) minutes.
Extended self-test routine
recommended polling time:        (   1) minutes.
Conveyance self-test routine
recommended polling time:        (   1) minutes.
 
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
  1 Raw_Read_Error_Rate     0x0000   100   100   000    Old_age   Offline      -       0
  5 Reallocated_Sector_Ct   0x0000   100   100   000    Old_age   Offline      -       0
  9 Power_On_Hours          0x0000   100   100   000    Old_age   Offline      -       202
12 Power_Cycle_Count       0x0000   100   100   000    Old_age   Offline      -       16
160 Uncorrectable_Error_Cnt 0x0000   100   100   000    Old_age   Offline      -       0
161 Valid_Spare_Block_Cnt   0x0000   100   100   000    Old_age   Offline      -       138
163 Initial_Bad_Block_Count 0x0000   100   100   000    Old_age   Offline      -       27
164 Total_Erase_Count       0x0000   100   100   000    Old_age   Offline      -       33759
165 Max_Erase_Count         0x0000   100   100   000    Old_age   Offline      -       24
166 Min_Erase_Count         0x0000   100   100   000    Old_age   Offline      -       0
167 Average_Erase_Count     0x0000   100   100   000    Old_age   Offline      -       16
168 Max_Erase_Count_of_Spec 0x0000   100   100   000    Old_age   Offline      -       3000
169 Remaining_Lifetime_Perc 0x0000   100   100   000    Old_age   Offline      -       100
175 Program_Fail_Count_Chip 0x0000   100   100   000    Old_age   Offline      -       0
176 Erase_Fail_Count_Chip   0x0000   100   100   000    Old_age   Offline      -       0
177 Wear_Leveling_Count     0x0000   100   100   050    Old_age   Offline      -       0
178 Runtime_Invalid_Blk_Cnt 0x0000   100   100   000    Old_age   Offline      -       0
181 Program_Fail_Cnt_Total  0x0000   100   100   000    Old_age   Offline      -       0
182 Erase_Fail_Count_Total  0x0000   100   100   000    Old_age   Offline      -       0
192 Power-Off_Retract_Count 0x0000   100   100   000    Old_age   Offline      -       4
194 Temperature_Celsius     0x0000   100   100   000    Old_age   Offline      -       30
195 Hardware_ECC_Recovered  0x0000   100   100   000    Old_age   Offline      -       229
196 Reallocated_Event_Count 0x0000   100   100   016    Old_age   Offline      -       0
197 Current_Pending_Sector  0x0000   100   100   000    Old_age   Offline      -       0
198 Offline_Uncorrectable   0x0000   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0000   100   100   050    Old_age   Offline      -       0
232 Available_Reservd_Space 0x0000   100   100   000    Old_age   Offline      -       100
241 Host_Writes_32MiB       0x0000   100   100   000    Old_age   Offline      -       175763
242 Host_Reads_32MiB        0x0000   100   100   000    Old_age   Offline      -       308024
245 TLC_Writes_32MiB        0x0000   100   100   000    Old_age   Offline      -       270072
 
SMART Error Log Version: 1
No Errors Logged
 
SMART Self-test log structure revision number 1
No self-tests have been logged.  [To run self-tests, use: smartctl -t]
 
 
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
    6        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.
 
Please help!
 
Kind Regards,
Todd

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Does CentOS 7.4 support the TRIM command? I couldn't find that data on Wikipedia - the TRIM page doesn't mention CentOS among the supporting OSes, and the CentOS page doesn't mention TRIM.

If it were running without TRIM, the SSD would be preserving lots of deleted files. And you'd presently see delays while it preps pending sectors for writing. Which would go away once the SSD's housecleaning caught up.

If this were the case, you could briefly run each SSD on a system supporting TRIM and your filesystem, to clear all the free blocks. Or change out your SSDs for larger ones, with far more free blocks to buffer you against the problem. Or of course, bug the CentOS devs to add TRIM support.

Edited by reader50

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