Just wanted to check if this was a big error, or a little error. If I should replace the drive right away, or just "be prepared" to replace it. This drive, like all the others, was a Western Digital external USB drive that I cracked open and installed into the unRaid server.

 

Quote

ATA Error Count: 1
	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 1 occurred at disk power-on lifetime: 3580 hours (149 days + 4 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 53 00 ff ff ff 0f  Error: UNC at LBA = 0x0fffffff = 268435455

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC   Powered_Up_Time  Command/Feature_Name
  -- -- -- -- -- -- -- --  ----------------  --------------------
  25 00 28 ff ff ff ef 00   9d+20:54:35.112  READ DMA EXT
  25 00 20 ff ff ff ef 00   9d+20:54:35.050  READ DMA EXT
  25 00 10 ff ff ff ef 00   9d+20:54:35.023  READ DMA EXT
  25 00 40 ff ff ff ef 00   9d+20:54:34.993  READ DMA EXT
  25 00 40 ff ff ff ef 00   9d+20:54:34.991  READ DMA EXT

 

Would be best to post the complete SMART report, but a single UNC error, especially with a bogus LBA might not be a reason for concern, at least not for now.

ST8000DM004-2CX188_WCT01MFN-20180313-0025.txt

Only attribute of concern is that single UNC error:

 

187 Reported_Uncorrect      -O--CK   099   099   000    -    1

 

Keep an eye on it, if there are more similar errors, or an UNC error with a valid LBA address, i.e., not LBA = 0x0fffffff, it might be prudent to replace it.