SMART, RAID and real world experience of failures.

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Hi all,

Extremely long time listener but very few time poster.

I got a SMART error email yesterday from my home server with a 4 x 1Tb RAID6. It basically boiled down to:

The following warning/error was logged by the smartd daemon:
Device: /dev/sdd [SAT], 1 Currently unreadable (pending) sectors
Device: /dev/sdd [SAT], 1 Offline uncorrectable sectors

This got me wondering so I ran a long test (smartctl -t long /dev/sdd) and sure enough, after an hour or so I got this:

# 2 Extended offline Completed: read failure 50% 17465 1172842872

So, in the spirit of experimentation, I did the following:
# mdadm /dev/md2 --manage --fail /dev/sdd
# mdadm /dev/md2 --manage --remove /dev/sdd
# dd if=/dev/zero of=/dev/sdd bs=10M
# mdadm /dev/md2 --manage --add /dev/sdd
< a resync occurred here, afterwards >
# smartctl -t long /dev/sdd
< long wait >
# smartctl -a /dev/sdd

This is where it gets interesting. Although it originally logged an error, I now see the following (with lots of other info trimmed):

ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 4 Start_Stop_Count 0x0032 100 100 020 Old_age Always - 154 5 Reallocated_Sector_Ct 0x0033 100 100 036 Pre-fail Always - 0 9 Power_On_Hours 0x0032 081 081 000 Old_age Always - 17493 12 Power_Cycle_Count 0x0032 100 100 020 Old_age Always - 77 197 Current_Pending_Sector 0x0012 100 100 000 Old_age Always - 0 198 Offline_Uncorrectable 0x0010 100 100 000 Old_age Offline - 0

Then even more interesting:
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 without error 00% 17489 - # 2 Extended offline Completed: read failure 50% 17465 1172842872

This makes me ponder. Has the drive recovered? Has the sector with the read failure been remapped and hidden from view? Is it still (more?) likely to fail in the near future?

Steven Haigh

Email: netwiz@xxxxxxxxx
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