I just installed my first unraid system a couple of months ago and the online support for getting it going was fantastic.  I started with one parity and one data drive to see if I could get it working for my crashplan family backup and it worked great.  I wanted to add another drive (2TB) to the array, so I followed the instructions to run preclear in the background.  It started fine, but quickly slowed down considerably.  After running all night, it only completed 17% of the pre read portion.  The rate was running about 80-85 MB/s, but now it is down to 1.2 MB/s.  I stopped and restarted preclear, but it is still running slow.  I stopped the array and restarted my raid server, but no change.  I attached the syslog that shows the last reboot process this morning.  I took the log after I started preclear again, but I could not see any evidence of preclear running.  Is there another log I should look at (or post)?  I think there are some errors, but I do not know what they mean.  Any suggestions to get the speed back up or am I just impatient?

syslog.zip

Preclear logs are in folder /boot/preclear_reports

Thanks for the log location.  How do I access that log while preclear is running?

 

After I wrote the first question, I started getting some syslog errors (attached).  Can anyone help interpreting the logs?  Does this indicate the drive is bad?

syslog2.zip

Thanks for the log location.  How do I access that log while preclear is running?

 

After I wrote the first question, I started getting some syslog errors (attached).  Can anyone help interpreting the logs?  Does this indicate the drive is bad?

Media Errors (UNC errors) are un-correctable errors in reading sectors on the disk.  The sector contents do not match the checksum at the end of the sector.    Basically, the disk has unreadable sectors.

 

The unRAID OS keeps re-initializing the disk to see if that will help, but it does not in your case.  (It really slows things down though)

If you post the result of

smartctl -a /dev/sdd

and look for the parameters describing re-allocated sectors and sectors pending re-allocation we'll be able to judge how bad the disk is.

 

 

Here is the result of the smartctl command.  I see there are both reallocated and pending reallocation, but I do not know if that is a large number or not.

 

 

ID# ATTRIBUTE_NAME          FLAG    VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE

  1 Raw_Read_Error_Rate    0x002f  192  192  051    Pre-fail  Always      -      194082

  3 Spin_Up_Time            0x0027  247  229  021    Pre-fail  Always      -      9608

  4 Start_Stop_Count        0x0032  098  098  000    Old_age  Always      -      2858

  5 Reallocated_Sector_Ct  0x0033  187  187  140    Pre-fail  Always      -      99

  7 Seek_Error_Rate        0x002e  100  253  000    Old_age  Always      -      0

  9 Power_On_Hours          0x0032  092  092  000    Old_age  Always      -      6138

10 Spin_Retry_Count        0x0032  100  100  000    Old_age  Always      -      0

11 Calibration_Retry_Count 0x0032  100  100  000    Old_age  Always      -      0

12 Power_Cycle_Count      0x0032  100  100  000    Old_age  Always      -      889

192 Power-Off_Retract_Count 0x0032  200  200  000    Old_age  Always      -      50

193 Load_Cycle_Count        0x0032  197  197  000    Old_age  Always      -      10910

194 Temperature_Celsius    0x0022  121  097  000    Old_age  Always      -      31

196 Reallocated_Event_Count 0x0032  119  119  000    Old_age  Always      -      81

197 Current_Pending_Sector  0x0032  197  197  000    Old_age  Always      -      1011

198 Offline_Uncorrectable  0x0030  200  200  000    Old_age  Offline      -      0

199 UDMA_CRC_Error_Count    0x0032  200  200  000    Old_age  Always      -      0

200 Multi_Zone_Error_Rate  0x0008  011  001  000    Old_age  Offline      -      37840

 

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  Short offline      Completed without error      00%      5985        -

# 2  Short offline      Completed: read failure      10%      5483        3905370078

# 3  Short offline      Completed without error      00%      5117        -

# 4  Short offline      Completed without error      00%      4795        -

# 5  Short offline      Completed without error      00%      4499        -

# 6  Short offline      Completed without error      00%      4261        -

# 7  Short offline      Completed without error      00%      3765        -

# 8  Short offline      Completed without error      00%      3498        -

# 9  Short offline      Completed without error      00%      3042        -

#10  Short offline      Completed without error      00%      2584        -

#11  Short offline      Completed without error      00%      2223        -

#12  Short offline      Completed without error      00%      1966        -

#13  Short offline      Completed without error      00%      1715        -

#14  Short offline      Completed without error      00%      462        -

#15  Short offline      Completed without error      00%      294        -

#16  Short offline      Completed without error      00%        39        -

 

SMART Selective self-test log data structure revision number 1

SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS

    1        0        0  Not_testing

    2        0        0  Not_testing

    3        0        0  Not_testing

    4        0        0  Not_testing

    5        0        0  Not_testing

Selective self-test flags (0x0):

  After scanning selected spans, do NOT read-scan remainder of disk.

If Selective self-test is pending on power-up, resume after 0 minute delay.

 

On a 'good' drive the pending reallocations should be zero, and normally the reallocated sectors is zero or a small number.  unRAID cannot successfully use drives that have pending sectors outstanding so if the pre-clear process is not resulting in the pending value being zero the drive should be RMA'ed.

Your disk is pretty bad.  RMA it.  Do not even think of using it with over 1000 unreadable sectors pending re-allocation.

Thanks.  Now I know why the preclear was so slow - it was struggling with a defective drive.  This afternoon it started getting even more errors.  It is only 33% done with the pre read and it has been running for over 8 hours.  I would lots rather find out the drive is bad now before I put any real data on it.  Even if unraid didn't require preclear before a new drive could be added to an array, now I understand why it would be a good idea to run anyway.  Thanks for your help with the logs.