Not so S.M.A.R.T.?

Today I sent the following question to Alsoft’s (DiskWarrior) support:

„I noticed entries like this one in my system.log:

May 31 10:11:53 tyrion
/Applications/DiskWarrior.app/Contents/MacOS/DiskWarriorDaemon[932]: [Thu May 31
10:11:53 CEST 2012] : The spare blocks for ATA device 'ST31000528ASQ', serial
number '6VP319CR', appear to be exhausted. (Total Available: 36) (Use Attempts:
229)

I have researched the issue and was surprised that the DiskWarrior manual
doesn’t mention this at all. There is some anecdotal evidence on the web that a
message like that is an indicator for impending drive failure.

So I installed smartmontools, because I wanted to know more details about the
drive’s state. Here’s the relevant output I got:

sudo smartctl -A disk0
smartctl 5.42 2011-10-20 r3458 [i386-apple-darwin10.8.0] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
1 Raw_Read_Error_Rate     0x000e   106   099   006    Old_age   Always       -       11960322
3 Spin_Up_Time            0x0003   100   100   000    Pre-fail  Always       -       0
4 Start_Stop_Count        0x0032   100   100   020    Old_age   Always       -       33
5 Reallocated_Sector_Ct   0x0033   082   082   036    Pre-fail  Always       -       741
7 Seek_Error_Rate         0x000f   084   060   030    Pre-fail  Always       -       246300939
9 Power_On_Hours          0x0032   078   078   000    Old_age   Always       -       19671
10 Spin_Retry_Count        0x0013   100   100   097    Pre-fail  Always       -       0
12 Power_Cycle_Count       0x0032   100   100   020    Old_age   Always       -       44
184 End-to-End_Error        0x0032   100   100   099    Old_age   Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0
188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       0
189 High_Fly_Writes         0x003a   100   100   000    Old_age   Always       -       0
190 Airflow_Temperature_Cel 0x0022   046   042   045    Old_age   Always   In_the_past 54 (1 165 58 35 0)
194 Temperature_Celsius     0x0022   054   058   000    Old_age   Always       -       54 (0 9 0 0 0)
195 Hardware_ECC_Recovered  0x001a   034   021   000    Old_age   Always       -       11960322
197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0010   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always       -       0

From my understanding of the manpage, the actual count of reallocated blocks (as
given by attribute 5) is 741, and the „value“ of 82 is still well above the
critical threshold of 36. What’s more, the attribute 197 shows there are zero
„current pending sectors“, which I understand to mean that all reallocation
requests could be satisfied so far. This seems to run counter to the output of
DiskWarriorDaemon. Could you please explain the discrepancy? Should I replace
the drive after all?“

Their reply was short: „You should replace this hard drive.“

That’s fine (I should be able to replace the drive under AppleCare), but a little low on details. Can anyone explain to me why the output of smartctl seems to be so different? Where do DiskWarrior’s numbers come from?

4 Gedanken zu „Not so S.M.A.R.T.?“

  1. The „229 use attempts“ appears to be the low 8 bits of the raw value.
    741 mod 256 = 229.

    As you commented, the reallocated sector count is well within acceptable limits, especially for a 20000 hour old disk, and in this case I would only be concerned if the reallocated sector count were rapidly increasing.

    However, I would also look at cooling – your HDD has reached 58C in the past.

    1. Thanks for your reply. Your idea regarding the value of 229 makes sense. The message from DiskWarriorDaemon seems to have been caused by a software malfunction anyway, because it never came back after a reboot. I’ve noticed the temperature as well – the maximum is up to 59C now, but there isn’t much I can do about that: it’s an iMac.

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