What type of error is Offline_Uncorrectable tracking?

Hi,

I'm trying to determine if a hard disk someone gave to me is reliable enough to use. It's a WDC WD4000F9YZ-09N20L0 (4TB Western Digital Enterprise). The drive originally had the following SMART stats:

Code:: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x002f 199 199 051 Pre-fail Always - 80 3 Spin_Up_Time 0x0027 184 184 021 Pre-fail Always - 9766 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 92 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 084 084 000 Old_age Always - 11768 10 Spin_Retry_Count 0x0032 100 253 000 Old_age Always - 0 11 Calibration_Retry_Count 0x0032 100 253 000 Old_age Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 92 183 Runtime_Bad_Block 0x0032 095 095 000 Old_age Always - 5 192 Power-Off_Retract_Count 0x0032 200 200 000 Old_age Always - 64 193 Load_Cycle_Count 0x0032 200 200 000 Old_age Always - 27 194 Temperature_Celsius 0x0022 116 097 000 Old_age Always - 36 196 Reallocated_Event_Count 0x0032 200 200 000 Old_age Always - 0 197 Current_Pending_Sector 0x0032 200 200 000 Old_age Always - 16 198 Offline_Uncorrectable 0x0030 200 200 000 Old_age Offline - 20 199 UDMA_CRC_Error_Count 0x0032 200 200 000 Old_age Always - 0 200 Multi_Zone_Error_Rate 0x0008 200 200 000 Old_age Offline - 33

I decided the first thing I would do with it was run badblocks (linux) on it as an easy way to write the entire drive a couple times. If it's going to die, I wanted to kill it right away. After the first write pass (badblocks -svw) the SMART stats related to reallocation changed. Nothing changed during the second pass. Now it looks like this:

Code:: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x002f 200 198 051 Pre-fail Always - 0 3 Spin_Up_Time 0x0027 184 184 021 Pre-fail Always - 9766 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 92 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 084 084 000 Old_age Always - 11795 10 Spin_Retry_Count 0x0032 100 253 000 Old_age Always - 0 11 Calibration_Retry_Count 0x0032 100 253 000 Old_age Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 92 183 Runtime_Bad_Block 0x0032 095 095 000 Old_age Always - 5 192 Power-Off_Retract_Count 0x0032 200 200 000 Old_age Always - 64 193 Load_Cycle_Count 0x0032 200 200 000 Old_age Always - 28 194 Temperature_Celsius 0x0022 105 097 000 Old_age Always - 47 196 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 200 200 000 Old_age Offline - 20 199 UDMA_CRC_Error_Count 0x0032 200 200 000 Old_age Always - 0 200 Multi_Zone_Error_Rate 0x0008 200 200 000 Old_age Offline - 33

I understand how pending reallocation works., but I don't understand what Offline_Uncorrectable is indicating. So, I have a couple questions.

1) What exactly is Offline_Uncorrectable?
2) Is it possible for that value to decrease? Under what circumstances would this happen?

The only other thing noteworthy thing I've seen so far is that I have 2 of these disks and started running badblocks at exactly the same time. The above disk has been running slightly slower that the other. It's approximately 3% behind the other which is (very roughly) 15-20 minutes of work.

Any thoughts?

Ryan

P.S. I like your posting guidelines :-)