No errors here, a few errors there... would you shuck it?

[TyantA]

I picked up 2x 12TB WD Elements drives and ran 3 preclear cycles on each (which took 9+ days) over USB. 

• Both finished successfully. 
• I checked before and after SMART values; nothing jumping out at me. (see here)
• I was about to unplug the drive & shuck it when I clicked the preclear log and see countless entries like this: 

Dec 8 03:21:13 XXXX kernel: sd 0:0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x07 driverbyte=0x00
Dec 8 03:21:13 XXXX kernel: sd 0:0:0:0: [sda] tag#0 CDB: opcode=0x88 88 00 00 00 00 05 25 96 70 00 00 00 08 00 00 00
Dec 8 03:21:13 XXXX kernel: print_req_error: I/O error, dev sda, sector 22105452544

I/O error for many, many sectors? Why is this not obvious in the SMART report?

 

• The second drive is full of the same. 
• I can't check its SMART values from the Dashboard because for some reason it doesn't show up under unassigned devices. Only sda does. (But both show up under "Main".