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gmirror - recovering from a failed HDD 30 August 2008
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I like RAID. On my development server, I use both hardware and software RAID. For hardware RAID on FreeBSD, I like 3Ware. For software RAID, I tend to use gmirror, because I don't need more than RAID-1.

Some time ago I added two 120GB HDD to this system. One was SATA, one was PATA. They were joined together via gmirror. Tonight I received some errors that one of the drives was failing. I replaced the drive, and recovered the mirror. I'll show you what I did, mostly so I know what to do the next time it happens, but also so you can see what to do as well.

You may wish to read Adding gmirror to an existing installation first.

The errors

The errors I encountered were (reformatted to better fit):

Aug 30 00:10:20 ngaio kernel: ad0: FAILURE - READ_DMA status=51<READY,DSC,ERROR>
                              error=40<UNCORRECTABLE> LBA=82797535
Aug 30 00:10:20 ngaio kernel: GEOM_MIRROR: Request failed (error=5). ad0
                              [READ(offset=42392337920, length=2048)]
Aug 30 00:10:20 ngaio kernel: GEOM_MIRROR: Device gm0: provider ad0 disconnected.

The following command identified the HDD in question:

# atacontrol list
ATA channel 0:
    Master:  ad0 <SAMSUNG SP1203N/TL100-30> ATA/ATAPI revision 7
By 'identified', I mean I knew which HDD to look for. There was only one Samsung in the machine.

Checking the gmirror status I saw:

# gmirror status
      Name    Status  Components
mirror/gm0  DEGRADED  ad3

In addition, I installed sysutils/smartmontools and got the following output:

# /usr/local/sbin/smartctl -a /dev/ad0
smartctl version 5.38 [i386-portbld-freebsd6.3] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Model Family:     SAMSUNG SpinPoint P80 series
Device Model:     SAMSUNG SP1203N
Serial Number:    S00QJ10Y282854
Firmware Version: TL100-30
User Capacity:    120,060,444,672 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   7
ATA Standard is:  ATA/ATAPI-7 T13 1532D revision 0
Local Time is:    Sat Aug 30 01:32:29 2008 BST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x00) Offline data collection activity
                                        was never started.
                                        Auto Offline Data Collection: Disabled.
Self-test execution status:      (   0) The previous self-test routine completed
                                        without error or no self-test has ever
                                        been run.
Total time to complete Offline
data collection:                 (4500) seconds.
Offline data collection
capabilities:                    (0x1b) SMART execute Offline immediate.
                                        Auto Offline data collection on/off support.
                                        Suspend Offline collection upon new
                                        command.
                                        Offline surface scan supported.
                                        Self-test supported.
                                        No Conveyance Self-test supported.
                                        No Selective Self-test supported.
SMART capabilities:            (0x0003) Saves SMART data before entering
                                        power-saving mode.
                                        Supports SMART auto save timer.
Error logging capability:        (0x01) Error logging supported.
                                        No General Purpose Logging support.
Short self-test routine
recommended polling time:        (   1) minutes.
Extended self-test routine
recommended polling time:        (  75) minutes.

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000f   100   100   051    Pre-fail  Always       -       394
  3 Spin_Up_Time            0x0007   100   100   025    Pre-fail  Always       -       5888
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       5
  5 Reallocated_Sector_Ct   0x0033   100   100   011    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000f   100   100   051    Pre-fail  Always       -       0
  8 Seek_Time_Performance   0x0025   100   100   015    Pre-fail  Offline      -       0
  9 Power_On_Half_Minutes   0x0032   100   100   000    Old_age   Always       -       2656h+04m
 10 Spin_Retry_Count        0x0033   100   100   051    Pre-fail  Always       -       0
 11 Calibration_Retry_Count 0x0012   100   100   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       5
194 Temperature_Celsius     0x0022   103   091   000    Old_age   Always       -       45
195 Hardware_ECC_Recovered  0x001a   100   100   000    Old_age   Always       -       298614779
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       1
197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x000a   100   100   051    Old_age   Always       -       0
201 Soft_Read_Error_Rate    0x000a   100   100   051    Old_age   Always       -       6

SMART Error Log Version: 1
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: 2654 hours (110 days + 14 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 51 04 df 63 ef e4  Error: UNC 4 sectors at LBA = 0x04ef63df = 82797535

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC   Powered_Up_Time  Command/Feature_Name
  -- -- -- -- -- -- -- --  ----------------  --------------------
  c8 00 04 df 63 ef e4 00  13d+18:46:35.829  READ DMA
  c8 00 04 07 49 eb e4 00  13d+18:46:35.829  READ DMA
  c8 00 04 db 48 eb e4 00  13d+18:46:35.829  READ DMA
  c8 00 04 03 3b eb e4 00  13d+18:46:35.829  READ DMA
  c8 00 04 ab 3a eb e4 00  13d+18:46:35.829  READ DMA

SMART Self-test log structure revision number 1
No self-tests have been logged.  [To run self-tests, use: smartctl -t]


Device does not support Selective Self Tests/Logging
Interpreting the errors

I received conflicting advice regarding the above. One person said the disk was toast. Another said it should be able to recover from the above. I went with the easy bit, and replaced the HDD. Next was rebuilding the gmirror.

Rebuilding the array

My first attempt to insert a new HDD failed.

# gmirror insert gm0 /dev/ad6
Not all disks connected.

This isn't helpful, the first time you see it. I found my answer in a freebsd-geom mailing list post.

# gmirror forget gm0
# gmirror insert gm0 /dev/ad6
# gmirror status
       Name    Status  Components
mirror/gm0  DEGRADED  ad3
                      ad6 (0%)

It took about 45 minutes for the array to sync up. I like gmirror. :)


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