Some days ago I found that the partition related to my RAID 5 wasn't mounted. I examined my disks and I got:mdadm --examine /dev/sd{a,b,c,d}1mdadm: No md superblock detected on /dev/sda1./dev/sdb1:          Magic : a92b4efc        Version : 1.2    Feature Map : 0x0     Array UUID : 87fdc598:a995d0f7:41123bcf:e2760aeb           Name : itake:0  (local to host itake)  Creation Time : Tue Aug 28 17:44:52 2012     Raid Level : raid5   Raid Devices : 4 Avail Dev Size : 1953122952 (931.32 GiB 1000.00 GB)     Array Size : 2929683456 (2793.96 GiB 3000.00 GB)  Used Dev Size : 1953122304 (931.32 GiB 1000.00 GB)    Data Offset : 2048 sectors   Super Offset : 8 sectors   Unused Space : before=1968 sectors, after=648 sectors          State : clean    Device UUID : db15e0ad:ef9f28be:de5e5a5a:f929ebb9    Update Time : Sun Sep 11 00:00:26 2016       Checksum : 700e7a14 - correct         Events : 6141         Layout : left-symmetric     Chunk Size : 512K   Device Role : Active device 1   Array State : AA.A ('A' == active, '.' == missing, 'R' == replacing)/dev/sdc1:          Magic : a92b4efc        Version : 1.2    Feature Map : 0x0     Array UUID : 87fdc598:a995d0f7:41123bcf:e2760aeb           Name : itake:0  (local to host itake)  Creation Time : Tue Aug 28 17:44:52 2012     Raid Level : raid5   Raid Devices : 4 Avail Dev Size : 1953122952 (931.32 GiB 1000.00 GB)     Array Size : 2929683456 (2793.96 GiB 3000.00 GB)  Used Dev Size : 1953122304 (931.32 GiB 1000.00 GB)    Data Offset : 2048 sectors   Super Offset : 8 sectors   Unused Space : before=1968 sectors, after=648 sectors          State : clean    Device UUID : f3c74ca8:076e5078:305ad83b:159f048d    Update Time : Sun Sep  4 00:08:53 2016       Checksum : d9306794 - correct         Events : 5896         Layout : left-symmetric     Chunk Size : 512K   Device Role : Active device 2   Array State : AAAA ('A' == active, '.' == missing, 'R' == replacing)/dev/sdd1:          Magic : a92b4efc        Version : 1.2    Feature Map : 0x0     Array UUID : 87fdc598:a995d0f7:41123bcf:e2760aeb           Name : itake:0  (local to host itake)  Creation Time : Tue Aug 28 17:44:52 2012     Raid Level : raid5   Raid Devices : 4 Avail Dev Size : 1953122952 (931.32 GiB 1000.00 GB)     Array Size : 2929683456 (2793.96 GiB 3000.00 GB)  Used Dev Size : 1953122304 (931.32 GiB 1000.00 GB)    Data Offset : 2048 sectors   Super Offset : 8 sectors   Unused Space : before=1968 sectors, after=648 sectors          State : clean    Device UUID : 4b376772:29ca4f41:342d39df:877fece0    Update Time : Sun Sep 11 00:00:26 2016       Checksum : 639ce9a5 - correct         Events : 6141         Layout : left-symmetric     Chunk Size : 512K   Device Role : Active device 3   Array State : AA.A ('A' == active, '.' == missing, 'R' == replacing)  So I thought that only sda was damaged and I could recover the information. I bought a new disk and now I saw that it wasn't sda only but sdc as well. I wonder if there is any chance of try to repair any of two disks to try to recreate and recover the information before replace both...I leave here some useful information about the errors, if you need something else please let me knowcat /proc/mdstatPersonalities : [raid6] [raid5] [raid4]unused devices: <none>  cat /var/log/syslogNov 11 09:16:59 itake kernel: [   18.230695] sd 0:0:0:0: [sda] Unhandled sense codeNov 11 09:16:59 itake kernel: [   18.230698] sd 0:0:0:0: [sda]  Result: hostbyte=DID_OK driverbyte=DRIVER_SENSENov 11 09:16:59 itake kernel: [   18.230703] sd 0:0:0:0: [sda]  Sense Key : Medium Error [current] [descriptor]Nov 11 09:16:59 itake kernel: [   18.230708] Descriptor sense data with sense descriptors (in hex):Nov 11 09:16:59 itake kernel: [   18.230711]         72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00Nov 11 09:16:59 itake kernel: [   18.230721]         00 00 08 08Nov 11 09:16:59 itake kernel: [   18.230726] sd 0:0:0:0: [sda]  Add. Sense: Unrecovered read error - auto reallocate failedNov 11 09:16:59 itake kernel: [   18.230734] sd 0:0:0:0: [sda] CDB: Read(10): 28 00 00 00 08 08 00 00 08 00Nov 11 09:16:59 itake kernel: [   18.230744] end_request: I/O error, dev sda, sector 2056Nov 11 09:16:59 itake kernel: [   18.230796] Buffer I/O error on device sda1, logical block 1Nov 11 09:16:59 itake kernel: [   18.230881] ata1: EH complete...Nov 11 09:16:59 itake kernel: [  104.221334] sd 2:0:0:0: [sdc] Unhandled sense codeNov 11 09:16:59 itake kernel: [  104.221337] sd 2:0:0:0: [sdc]  Result: hostbyte=DID_OK driverbyte=DRIVER_SENSENov 11 09:16:59 itake kernel: [  104.221342] sd 2:0:0:0: [sdc]  Sense Key : Medium Error [current] [descriptor]Nov 11 09:16:59 itake kernel: [  104.221347] Descriptor sense data with sense descriptors (in hex):Nov 11 09:16:59 itake kernel: [  104.221350]         72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00Nov 11 09:16:59 itake kernel: [  104.221360]         74 70 68 00Nov 11 09:16:59 itake kernel: [  104.221365] sd 2:0:0:0: [sdc]  Add. Sense: Unrecovered read error - auto reallocate failedNov 11 09:16:59 itake kernel: [  104.221372] sd 2:0:0:0: [sdc] CDB: Read(10): 28 00 74 70 68 00 00 01 d0 00Nov 11 09:16:59 itake kernel: [  104.221381] end_request: I/O error, dev sdc, sector 1953523712Nov 11 09:16:59 itake kernel: [  104.221431] Buffer I/O error on device sdc, logical block 244190464Nov 11 09:16:59 itake kernel: [  104.221482] Buffer I/O error on device sdc, logical block 244190465Nov 11 09:16:59 itake kernel: [  104.221524] Buffer I/O error on device sdc, logical block 244190466Nov 11 09:16:59 itake kernel: [  104.221567] Buffer I/O error on device sdc, logical block 244190467Nov 11 09:16:59 itake kernel: [  104.221608] Buffer I/O error on device sdc, logical block 244190468Nov 11 09:16:59 itake kernel: [  104.221649] Buffer I/O error on device sdc, logical block 244190469Nov 11 09:16:59 itake kernel: [  104.221690] Buffer I/O error on device sdc, logical block 244190470Nov 11 09:16:59 itake kernel: [  104.221731] Buffer I/O error on device sdc, logical block 244190471Nov 11 09:16:59 itake kernel: [  104.221772] Buffer I/O error on device sdc, logical block 244190472Nov 11 09:16:59 itake kernel: [  104.221813] Buffer I/O error on device sdc, logical block 244190473Nov 11 09:16:59 itake kernel: [  104.221897] ata3: EH completeNov 11 09:16:59 itake kernel: [  107.652344] ata3.00: exception Emask 0x0 SAct 0x7 SErr 0x0 action 0x0Nov 11 09:16:59 itake kernel: [  107.652389] ata3.00: irq_stat 0x40000008Nov 11 09:16:59 itake kernel: [  107.652429] ata3.00: failed command: READ FPDMA QUEUEDNov 11 09:16:59 itake kernel: [  107.652474] ata3.00: cmd 60/08:00:d8:69:70/00:00:74:00:00/40 tag 0 ncq 4096 inNov 11 09:16:59 itake kernel: [  107.652476]          res 41/40:00:d8:69:70/00:00:74:00:00/40 Emask 0x409 (media error) <F>Nov 11 09:16:59 itake kernel: [  107.652559] ata3.00: status: { DRDY ERR }Nov 11 09:16:59 itake kernel: [  107.652598] ata3.00: error: { UNC }Nov 11 09:16:59 itake kernel: [  107.654733] ata3.00: configured for UDMA/133Nov 11 09:16:59 itake kernel: [  107.654754] ata3: EH complete...Nov 11 09:16:59 itake kernel: [  137.768972] sd 0:0:0:0: [sda]  Add. Sense: Unrecovered read error - auto reallocate failedNov 11 09:16:59 itake kernel: [  137.768979] sd 0:0:0:0: [sda] CDB: Read(10): 28 00 00 00 08 08 00 00 08 00Nov 11 09:16:59 itake kernel: [  137.768989] end_request: I/O error, dev sda, sector 2056Nov 11 09:16:59 itake kernel: [  137.769067] ata1: EH completeNov 11 09:16:59 itake kernel: [  137.779624] md: md0 stopped.Nov 11 09:16:59 itake kernel: [  138.630989] ata3.00: exception Emask 0x0 SAct 0x3 SErr 0x0 action 0x0Nov 11 09:16:59 itake kernel: [  138.631035] ata3.00: irq_stat 0x40000008Nov 11 09:16:59 itake kernel: [  138.631076] ata3.00: failed command: READ FPDMA QUEUEDNov 11 09:16:59 itake kernel: [  138.631121] ata3.00: cmd 60/08:00:40:68:70/00:00:74:00:00/40 tag 0 ncq 4096 inNov 11 09:16:59 itake kernel: [  138.631123]          res 41/40:00:40:68:70/00:00:74:00:00/40 Emask 0x409 (media error) <F>Nov 11 09:16:59 itake kernel: [  138.631206] ata3.00: status: { DRDY ERR }Nov 11 09:16:59 itake kernel: [  138.631245] ata3.00: error: { UNC }Nov 11 09:16:59 itake kernel: [  138.633417] ata3.00: configured for UDMA/133Nov 11 09:16:59 itake kernel: [  138.633443] ata3: EH completeNov 11 09:16:59 itake kernel: [  138.637684] md: bind<sdc1>Nov 11 09:16:59 itake kernel: [  138.637896] md: bind<sdd1>Nov 11 09:16:59 itake kernel: [  138.638139] md: bind<sdb1>Nov 11 09:16:59 itake kernel: [  138.638173] md: kicking non-fresh sdc1 from array!Nov 11 09:16:59 itake kernel: [  138.638180] md: unbind<sdc1>Nov 11 09:16:59 itake kernel: [  138.640178] md: export_rdev(sdc1)Nov 11 09:16:59 itake kernel: [  138.640178] md: export_rdev(sdc1)Nov 11 09:16:59 itake kernel: [  138.708065] raid6: int64x1   1355 MB/sNov 11 09:16:59 itake kernel: [  138.776062] raid6: int64x2   1504 MB/sNov 11 09:16:59 itake kernel: [  138.844062] raid6: int64x4   1284 MB/sNov 11 09:16:59 itake kernel: [  138.912061] raid6: int64x8   1109 MB/sNov 11 09:16:59 itake kernel: [  138.980085] raid6: sse2x1    2124 MB/sNov 11 09:16:59 itake kernel: [  139.048065] raid6: sse2x2    3413 MB/sNov 11 09:16:59 itake kernel: [  139.116061] raid6: sse2x4    4022 MB/sNov 11 09:16:59 itake kernel: [  139.116064] raid6: using algorithm sse2x4 (4022 MB/s)Nov 11 09:16:59 itake kernel: [  139.116302] async_tx: api initialized (async)Nov 11 09:16:59 itake kernel: [  139.116471] xor: automatically using best checksumming function: generic_sseNov 11 09:16:59 itake kernel: [  139.136056]    generic_sse:  6183.000 MB/secNov 11 09:16:59 itake kernel: [  139.136059] xor: using function: generic_sse (6183.000 MB/sec)Nov 11 09:16:59 itake kernel: [  139.137667] md: raid6 personality registered for level 6Nov 11 09:16:59 itake kernel: [  139.137671] md: raid5 personality registered for level 5Nov 11 09:16:59 itake kernel: [  139.137674] md: raid4 personality registered for level 4Nov 11 09:16:59 itake kernel: [  139.137936] bio: create slab <bio-1> at 1Nov 11 09:16:59 itake kernel: [  139.137960] md/raid:md0: device sdb1 operational as raid disk 1Nov 11 09:16:59 itake kernel: [  139.137964] md/raid:md0: device sdd1 operational as raid disk 3Nov 11 09:16:59 itake kernel: [  139.138427] md/raid:md0: allocated 4280kBNov 11 09:16:59 itake kernel: [  139.138551] md/raid:md0: not enough operational devices (2/4 failed)Nov 11 09:16:59 itake kernel: [  139.138628] RAID conf printout:Nov 11 09:16:59 itake kernel: [  139.138630]  --- level:5 rd:4 wd:2Nov 11 09:16:59 itake kernel: [  139.138634]  disk 1, o:1, dev:sdb1Nov 11 09:16:59 itake kernel: [  139.138637]  disk 3, o:1, dev:sdd1Nov 11 09:16:59 itake kernel: [  139.139106] md/raid:md0: failed to run raid set.Nov 11 09:16:59 itake kernel: [  139.139146] md: pers->run() failed ...Nov 11 09:16:59 itake kernel: [  139.139523] md: md0 stopped.Nov 11 09:16:59 itake kernel: [  139.139532] md: unbind<sdb1>Nov 11 09:16:59 itake kernel: [  139.156130] md: export_rdev(sdb1)Nov 11 09:16:59 itake kernel: [  139.156158] md: unbind<sdd1>Nov 11 09:16:59 itake kernel: [  139.168118] md: export_rdev(sdd1)...smartctl -a /dev/sdasmartctl 6.5 2016-01-24 r4214 [x86_64-linux-3.2.0-4-amd64] (local build)Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org=== START OF INFORMATION SECTION ===Model Family:     SAMSUNG SpinPoint F3Device Model:     SAMSUNG HD103SJSerial Number:    S246J1KZ410348LU WWN Device Id: 5 0024e9 0034ebb37Firmware Version: 1AJ10001User Capacity:    1,000,203,804,160 bytes [1.00 TB]Sector Size:      512 bytes logical/physicalRotation Rate:    7200 rpmForm Factor:      3.5 inchesDevice is:        In smartctl database [for details use: -P show]ATA Version is:   ATA8-ACS T13/1699-D revision 6SATA Version is:  SATA 2.6, 3.0 Gb/sLocal Time is:    Fri Nov 11 11:17:00 2016 CETSMART support is: Available - device has SMART capability.SMART support is: Enabled=== START OF READ SMART DATA SECTION ===SMART overall-health self-assessment test result: PASSEDGeneral SMART Values:Offline data collection status:  (0x00) Offline data collection activity                    was never started.                    Auto Offline Data Collection: Disabled.Self-test execution status:      ( 121) The previous self-test completed having                    the read element of the test failed.Total time to complete Offlinedata collection:        ( 9300) seconds.Offline data collectioncapabilities:            (0x5b) 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.                    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.                    General Purpose Logging supported.Short self-test routinerecommended polling time:    (   2) minutes.Extended self-test routinerecommended polling time:    ( 155) minutes.SCT capabilities:          (0x003f) SCT Status supported.                    SCT Error Recovery Control supported.                    SCT Feature Control supported.                    SCT Data Table supported.SMART Attributes Data Structure revision number: 16Vendor Specific SMART Attributes with Thresholds:ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE  1 Raw_Read_Error_Rate     0x002f   100   100   051    Pre-fail  Always       -       784  2 Throughput_Performance  0x0026   252   252   000    Old_age   Always       -       0  3 Spin_Up_Time            0x0023   070   069   025    Pre-fail  Always       -       9385  4 Start_Stop_Count        0x0032   099   099   000    Old_age   Always       -       1225  5 Reallocated_Sector_Ct   0x0033   252   252   010    Pre-fail  Always       -       0  7 Seek_Error_Rate         0x002e   252   252   051    Old_age   Always       -       0  8 Seek_Time_Performance   0x0024   252   252   015    Old_age   Offline      -       0  9 Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       30077 10 Spin_Retry_Count        0x0032   252   252   051    Old_age   Always       -       0 11 Calibration_Retry_Count 0x0032   252   252   000    Old_age   Always       -       0 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       212191 G-Sense_Error_Rate      0x0022   252   252   000    Old_age   Always       -       0192 Power-Off_Retract_Count 0x0022   252   252   000    Old_age   Always       -       0194 Temperature_Celsius     0x0002   064   052   000    Old_age   Always       -       21 (Min/Max 11/48)195 Hardware_ECC_Recovered  0x003a   100   100   000    Old_age   Always       -       0196 Reallocated_Event_Count 0x0032   252   252   000    Old_age   Always       -       0197 Current_Pending_Sector  0x0032   100   100   000    Old_age   Always       -       2198 Offline_Uncorrectable   0x0030   252   252   000    Old_age   Offline      -       0199 UDMA_CRC_Error_Count    0x0036   200   200   000    Old_age   Always       -       0200 Multi_Zone_Error_Rate   0x002a   100   100   000    Old_age   Always       -       64223 Load_Retry_Count        0x0032   252   252   000    Old_age   Always       -       0225 Load_Cycle_Count        0x0032   100   100   000    Old_age   Always       -       1244SMART Error Log Version: 1No Errors LoggedSMART Self-test log structure revision number 1Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error# 1  Short offline       Completed: read failure       90%     30077         2056# 2  Extended offline    Completed: read failure       90%     30077         2056SMART Selective self-test log data structure revision number 0Note: revision number not 1 implies that no selective self-test has ever been run SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS    1        0        0  Completed_read_failure [90% left] (0-65535)    2        0        0  Not_testing    3        0        0  Not_testing    4        0        0  Not_testing    5        0        0  Not_testingSelective 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.smartctl -a /dev/sdcsmartctl 6.5 2016-01-24 r4214 [x86_64-linux-3.2.0-4-amd64] (local build)Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org=== START OF INFORMATION SECTION ===Model Family:     Western Digital GreenDevice Model:     WDC WD10EZRX-00A8LB0Serial Number:    WD-WMC1U5433779LU WWN Device Id: 5 0014ee 657f09173Firmware Version: 01.01A01User Capacity:    1,000,204,886,016 bytes [1.00 TB]Sector Sizes:     512 bytes logical, 4096 bytes physicalDevice is:        In smartctl database [for details use: -P show]ATA Version is:   ATA8-ACS (minor revision not indicated)SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 3.0 Gb/s)Local Time is:    Fri Nov 11 11:17:08 2016 CETSMART support is: Available - device has SMART capability.SMART support is: Enabled=== START OF READ SMART DATA SECTION ===SMART overall-health self-assessment test result: PASSEDGeneral SMART Values:Offline data collection status:  (0x85) Offline data collection activity                    was aborted by an interrupting command from host.                    Auto Offline Data Collection: Enabled.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 Offlinedata collection:        (12960) seconds.Offline data collectioncapabilities:            (0x7b) SMART execute Offline immediate.                    Auto Offline data collection on/off support.                    Suspend Offline collection upon new                    command.                    Offline surface scan supported.                    Self-test supported.                    Conveyance Self-test supported.                    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.                    General Purpose Logging supported.Short self-test routinerecommended polling time:    (   2) minutes.Extended self-test routinerecommended polling time:    ( 148) minutes.Conveyance self-test routinerecommended polling time:    (   5) minutes.SCT capabilities:          (0x30b5) SCT Status supported.                    SCT Feature Control supported.                    SCT Data Table supported.SMART Attributes Data Structure revision number: 16Vendor Specific SMART Attributes with Thresholds:ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       6787  3 Spin_Up_Time            0x0027   139   137   021    Pre-fail  Always       -       4041  4 Start_Stop_Count        0x0032   096   096   000    Old_age   Always       -       4454  5 Reallocated_Sector_Ct   0x0033   171   171   140    Pre-fail  Always       -       1262  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0  9 Power_On_Hours          0x0032   054   054   000    Old_age   Always       -       33859 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       -       145192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       31193 Load_Cycle_Count        0x0032   170   170   000    Old_age   Always       -       90973194 Temperature_Celsius     0x0022   119   104   000    Old_age   Always       -       24196 Reallocated_Event_Count 0x0032   001   001   000    Old_age   Always       -       819197 Current_Pending_Sector  0x0032   198   198   000    Old_age   Always       -       326198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       80SMART Error Log Version: 1ATA Error Count: 11 (device log contains only the most recent five errors)    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 asDDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes,SS=sec, and sss=millisec. It wraps after 49.710 days.Error 11 occurred at disk power-on lifetime: 33842 hours (1410 days + 2 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 60 b0 a8 d7 e1  Error: UNC 96 sectors at LBA = 0x01d7a8b0 = 30910640  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 60 a0 a8 d7 e1 08  17d+13:32:19.391  READ DMA  ef 10 02 00 00 00 a0 08  17d+13:32:19.391  SET FEATURES [Enable SATA feature]  ec 00 00 00 00 00 a0 08  17d+13:32:19.390  IDENTIFY DEVICE  ef 03 46 00 00 00 a0 08  17d+13:32:19.390  SET FEATURES [Set transfer mode]Error 10 occurred at disk power-on lifetime: 33842 hours (1410 days + 2 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 60 c8 a8 d7 e1  Error: UNC 96 sectors at LBA = 0x01d7a8c8 = 30910664  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 60 a0 a8 d7 e1 08  17d+13:32:11.498  READ DMA  ef 10 02 00 00 00 a0 08  17d+13:32:11.498  SET FEATURES [Enable SATA feature]  ec 00 00 00 00 00 a0 08  17d+13:32:11.497  IDENTIFY DEVICE  ef 03 46 00 00 00 a0 08  17d+13:32:11.497  SET FEATURES [Set transfer mode]Error 9 occurred at disk power-on lifetime: 33842 hours (1410 days + 2 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 60 a8 a8 d7 e1  Error: UNC 96 sectors at LBA = 0x01d7a8a8 = 30910632  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 60 a0 a8 d7 e1 08  17d+13:32:07.412  READ DMA  c8 00 08 98 a8 d7 e1 08  17d+13:32:07.412  READ DMAError 8 occurred at disk power-on lifetime: 33841 hours (1410 days + 1 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 08 48 f9 80 e1  Error: UNC 8 sectors at LBA = 0x0180f948 = 25229640  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 08 48 f9 80 e1 08  17d+13:12:31.938  READ DMA  ef 10 02 00 00 00 a0 08  17d+13:12:31.938  SET FEATURES [Enable SATA feature]  ec 00 00 00 00 00 a0 08  17d+13:12:31.937  IDENTIFY DEVICE  ef 03 46 00 00 00 a0 08  17d+13:12:31.937  SET FEATURES [Set transfer mode]Error 7 occurred at disk power-on lifetime: 33841 hours (1410 days + 1 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 08 48 f9 80 e1  Error: UNC 8 sectors at LBA = 0x0180f948 = 25229640  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 08 48 f9 80 e1 08  17d+13:12:29.429  READ DMA  c8 00 b8 48 f5 80 e1 08  17d+13:12:29.410  READ DMASMART Self-test log structure revision number 1Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error# 1  Extended offline    Completed: read failure       90%     33858         384848# 2  Short offline       Completed: read failure       80%     33857         1951525160SMART 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_testingSelective 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.EDITI cloned sda disk using:ddrescue -d -f -r3 /dev/sda /dev/sde ddrescue.logfileGNU ddrescue 1.19Initial status (read from logfile)rescued:     1000 GB,  errsize:    4096 B,  errors:       3Current statusrescued:     1000 GB,  errsize:    4096 B,  current rate:        0 B/s   ipos:     1052 kB,   errors:       3,    average rate:        0 B/s   opos:     1052 kB, run time:    3.13 m,  successful read:    3.13 m agoBut the cloned disk sde says as well: mdadm: No md superblock detected on /dev/sde1. Could I recover those superblocks?
Recover software RAID5 data
hard disk;data recovery;raid;mdadm;software raid
We need to split your problem into two:Rebuild the array for missing /dev/sda superblock.Handle the damaged data on /dev/sdcRebuilding the arrayI presume that the 4kB block not recovered from /dev/sda was the superblock, because your partition started at 1MiB (2048 sectors), and the superblock started at +8 sectors into the partition (2056 sectors), exactly on the 2056 sector mark where the bad sector exists. The assumption is that the REST of the data on that drive is 100% intact.The problem with --assume-clean in general, is that you need to be extremely careful that the parameters exactly match what would have been used at the time the array was created. Changes in default values since your array creation date of Tue Aug 28 17:44:52 2012 are your ENEMY here. Metadata version, bitmap assumption (devices larger than 100GB get them automatically now), raid layout, etc.If you're not absolutely certain, I would strongly suggest cloning ALL 4 of the drives to else (in an absolute pinch you could even use a single drive with 4 partitions each of 1TB/1953122952 sectors), and trying to re-assemble that instead. As /dev/sda is starting to fail as well as /dev/sdc, and you probably bought all your drives at the same time, maybe even two complete copies of the data, in case you have a further drive failure in trying to recover (depends on how valuable you consider your data).If assume-clean works on the test copy, you're well-placed to move it elsewhere.Here's some script help for you, distilling what you gave above (note that --examine reports in units of sectors for some values, but --create takes in units of KiB).#!/bin/bash# Facts we know about your array, from your mdadm -E output.num_devices=4num_spares=0chunk_size=512 # KiBdata_offset=1024 # KiBdrive_size=976561152 # KiBuuid=87fdc598:a995d0f7:41123bcf:e2760aebmetadata_ver=1.2name=itake:0bitmap=noneoriginal_device_order=(/dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1)# I assume you recovered:# /dev/sda to /dev/sde# /dev/sdc to /dev/sdf# If not, adjust as needed.## Read all the way to the bottom of my response first, because you# MIGHT want to use 'missing' in place of /dev/sdf1 initially.new_device_order=(/dev/sde1 /dev/sdb1 /dev/sdf1 /dev/sdd1)mdadm --create /dev/md0 \--level 5 --layout left-symmetric-n $num_devices -x $num_spares \--uuid $uuid \--metadata $metadata_ver \--chunk $chunk_size--size $drive_size \--data-offset $data_offset \--name $name \--bitmap $bitmap \${new_device_order[@]}  Scrubbing the array (option 1)We know /dev/sdc had bad sectors in the middle of your data area, and as a slightly more nuclear option, you could pass missing in place of /dev/sdf1 during the array creation, and then do mdadm --add /dev/md0 /dev/sdf1 to force a rebuild from the other devices onto /dev/sdf1.Scrubbing the array (option 2)Now we need to fix up the fact that parts of /dev/sdc are gone, and in their place on /dev/sdf, there are just zeroed blocks.echo repair >/sys/devices/virtual/block/md0/md/sync_actionAt the end of this, you should have it repaired, but I'm not 100% certain of the behavior that will be taken to recovery those blocks.