Raid-Z2-Pool: Data still save when one HDD failed long SMART test?

[saveZFS]

Hallo,

I'm using TrueNAS since a few month as a backup for my Synology.
When I've practiced enough with TrueNAS, I want to use TrueNAS as the master and the Synology as the backup.
At the moment I use six older WD RED 4TB in a Raid-Z2.

Today I got this error message: "Device: /dev/da7 [SAT], Self-Test Log error count increased from 0 to 1"
It seems like the long SMART test failed. I post the SMART results at the end.

The question now is, will my data be absolutely safe unless another hard drive ends up failing or showing an error?
Or can this one HDD alone change the database in such a way that there can be defective bits or something similar?

Smart Log:
=== START OF INFORMATION SECTION ===
Model Family: Western Digital Red
Device Model: WDC WD40EFRX-68N32N0
Serial Number:
LU WWN Device Id:
Firmware Version: 82.00A82
User Capacity: 4,000,787,030,016 bytes [4.00 TB]
Sector Sizes: 512 bytes logical, 4096 bytes physical
Rotation Rate: 5400 rpm
Form Factor: 3.5 inches
Device is: In smartctl database [for details use: -P show]
ATA Version is: ACS-3 T13/2161-D revision 5
SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is: Fri Apr 1 21:09:48 2022 CEST
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: (45360) 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: ( 482) minutes.
Conveyance self-test routine
recommended polling time: ( 5) minutes.
SCT capabilities: (0x303d) 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 200 200 051 Pre-fail Always - 0
3 Spin_Up_Time 0x0027 228 162 021 Pre-fail Always - 3600
4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 328
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 049 049 000 Old_age Always - 37765
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 - 328
192 Power-Off_Retract_Count 0x0032 200 200 000 Old_age Always - 299
193 Load_Cycle_Count 0x0032 200 200 000 Old_age Always - 477
194 Temperature_Celsius 0x0022 115 097 000 Old_age Always - 35
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 100 253 000 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 - 19

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: read failure 90% 37745 41124664
# 2 Short offline Completed without error 00% 37721 -
# 3 Short offline Completed without error 00% 37697 -
# 4 Short offline Completed without error 00% 37673 -
# 5 Short offline Completed without error 00% 37649 -
# 6 Short offline Completed without error 00% 37626 -
# 7 Short offline Completed without error 00% 37602 -
# 8 Short offline Completed without error 00% 37578 -
# 9 Short offline Completed without error 00% 37554 -
#10 Short offline Completed without error 00% 37530 -
#11 Short offline Completed without error 00% 37506 -
#12 Short offline Completed without error 00% 37482 -
#13 Short offline Completed without error 00% 37458 -
#14 Short offline Completed without

 

[NugentS]

RAIDZ2 = two disks parity
If you lose one disk you are fine (but need to fix the issue)
If you lose two disks you are probably fine - but you have no parity left so certain functions to fix bit rot will not work
If you lose three disks then go out and get drunk and hope your backups are good

 

[saveZFS]

If you lose one disk you are fine (but need to fix the issue)

Thank you for your assessment. I was afraid that a read error could destroy something even with a defective disk in the pool!

So it can generally be said that a hard drive has to be replaced if a smart test fails?

Can I replace a WD Red HDD with a Segate or Toschiba as long as it has at least 4TB and uses CMR as recording technology?
Or should it always be the same hard drives?

 

[NugentS]

Yes you can replace with a different disk manufacturer with the caveats that you mention

Once you have replaced the disk run badblocks (or equivalent) in a full write cycle on the failing disk and see if it passes a long test afterwards. If it does then you have spare that you can use later (regard it with mild suspicion) - but it is a spare