Buffalo LS220D – lost drive (hiccup)

Yesterday I noticed that the LEDs were blinking amber on one of my LS220D boxes. My initial thought was that a disk had failed (it’s just a backup of my backup). Checked with the “NAS Navigator” application, and it stated that it was unable to mount the data array (md10) (I have not logged the full error message here, as I continued the attempts to solve the situation).

dmesg output

I logged in as root (see other posts) to check what had gone wrong.
‘dmesg’ revealed that a disk had been lost during smartctl (multiple repeats of the below content):

program smartctl is using a deprecated SCSI ioctl, please convert it to SG_IO
Unable to handle kernel NULL pointer dereference at virtual address 000000a4
pgd = c27d4000
[000000a4] *pgd=0fe93831, *pte=00000000, *ppte=00000000
Internal error: Oops: 817 [#50]
Modules linked in: usblp usb_storage ohci_hcd ehci_hcd xhci_hcd usbcore usb_common
CPU: 0    Tainted: G      D       (3.3.4 #1)
PC is at sg_scsi_ioctl+0xe0/0x374
LR is at sg_scsi_ioctl+0xcc/0x374
pc : []    lr : []    psr: 60000013
sp : cafb5d58  ip : 00000000  fp : 00000024
r10: 00000006  r9 : c41d1860  r8 : 00000012
r7 : 00000000  r6 : 00000024  r5 : beee5550  r4 : beee5548
r3 : cafb4000  r2 : cafb5d58  r1 : 00000000  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
Control: 10c5387d  Table: 027d4019  DAC: 00000015
Process smartctl (pid: 1027, stack limit = 0xcafb42e8)
Stack: (0xcafb5d58 to 0xcafb6000)
5d40:          c057c2b8 60000013
5d60: c21f27f0 beee5548 c2274800 0000005d cafb5de4 00000000 c998edcc 00000004
5d80: c99800c8 c00a6e64 c9d034e0 00000028 c998edc8 00000029 c27d4000 c00a8fc0
5da0: 00000000 00000000 00000000 c998ed08 c2274800 56e6994b beee5a48 beee5548
5dc0: 0000005d 0000005d c2274800 c21f27f0 cafb4000 56e6994b beee7e34 beee5548
5de0: 0000005d 0000005d c2274800 c21f27f0 cafb4000 ffffffed beee7e34 c0245494
5e00: 00000053 fffffffd 00002006 00000024 beee5af8 beee5ae0 beee5ab8 00004e20
5e20: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
5e40: c27d4000 00000000 c27d4000 cb0023e0 c87f3d30 00000028 beee7e34 c00be67c
5e60: c27d4000 00000028 cafb5fb0 56e6994b 00000001 0000005d c8014040 beee5548
5e80: 0000005d c0245530 beee5548 0000005d 00000001 00000001 beee5548 c222c000
5ea0: c8014040 c02a6284 beee5548 beee5548 c8014040 c2274800 00000001 0000005d
5ec0: 00000000 c02422a0 beee5548 c0242be0 00000000 cafb5f78 00000001 c2949000
5ee0: ffffff9c c8014040 00000000 00000007 c054ff34 00039db8 cafb5fb0 beee5548
5f00: c21e0470 00000003 00000003 c000e3c8 cafb4000 00000000 beee7e34 c00e0060
5f20: 00000000 00000000 cf34be00 2c1b812a 5e6a6136 2c1b812a cf1a2548 00000000
5f40: 00000000 00000000 00000003 00000003 c95a2ec0 c2949000 c95a2ec8 00000020
5f60: 00000003 c95a2ec0 beee5548 00000001 00000003 c000e3c8 cafb4000 00000000
5f80: beee7e34 c00e010c 00000003 00000000 beee5548 beee5548 0006d614 beee5a8c
5fa0: 00000036 c000e200 beee5548 0006d614 00000003 00000001 beee5548 00000000
5fc0: beee5548 0006d614 beee5a8c 00000036 00000000 00000003 00000006 beee7e34
5fe0: beee5ae0 beee5540 00039688 b6da5cec 80000010 00000003 cfcfcfcf 00000014
[] (sg_scsi_ioctl+0xe0/0x374) from [] (scsi_cmd_ioctl+0x39c/0x3fc)
[] (scsi_cmd_ioctl+0x39c/0x3fc) from [] (scsi_cmd_blk_ioctl+0x3c/0x44)
[] (scsi_cmd_blk_ioctl+0x3c/0x44) from [] (sd_ioctl+0x8c/0xb8)
[] (sd_ioctl+0x8c/0xb8) from [] (__blkdev_driver_ioctl+0x20/0x28)
[] (__blkdev_driver_ioctl+0x20/0x28) from [] (blkdev_ioctl+0x670/0x6c0)
[] (blkdev_ioctl+0x670/0x6c0) from [] (do_vfs_ioctl+0x49c/0x514)
[] (do_vfs_ioctl+0x49c/0x514) from [] (sys_ioctl+0x34/0x58)
[] (sys_ioctl+0x34/0x58) from [] (ret_fast_syscall+0x0/0x30)
Code: e1a0200d e7d3a2a8 e3c23d7f e3c3303f (e1c0aab4)
---[ end trace 660c9d3c9b4a9034 ]---

fdisk output

Using ‘fdisk’ (incorrect for this NAS), I listed the partitions on /dev/sda and /dev/sdb (nothing about /dev/sda):

[root@BUFFALO-4 ~]# fdisk -l /dev/sda
[root@BUFFALO-4 ~]# fdisk -l /dev/sdb

WARNING: GPT (GUID Partition Table) detected on '/dev/sdb'! The util fdisk doesn't support GPT. Use GNU Parted.

Disk /dev/sdb: 4000.8 GB, 4000787030016 bytes
255 heads, 63 sectors/track, 486401 cylinders, total 7814037168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1  4294967295  2147483647+  ee  GPT
Partition 1 does not start on physical sector boundary.

smartctl output

[root@BUFFALO-4 ~]# smartctl --scan
/dev/sda -d scsi # /dev/sda, SCSI device
/dev/sdb -d scsi # /dev/sdb, SCSI device

[root@BUFFALO-4 ~]# smartctl --all /dev/sda
smartctl 6.3 2014-07-26 r3976 [armv7l-linux-3.3.4] (local build)
Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org

Segmentation fault

[root@BUFFALO-4 ~]# smartctl --all /dev/sdb
smartctl 6.3 2014-07-26 r3976 [armv7l-linux-3.3.4] (local build)
Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Caviar Green (AF, SATA 6Gb/s)
Device Model:     WDC WD40EZRX-22SPEB0
Serial Number:    WD-WCC4E1UUZH74
LU WWN Device Id: 5 0014ee 2b768eeb4
Firmware Version: 80.00A80
User Capacity:    4,000,787,030,016 bytes [4.00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Rotation Rate:    5400 rpm
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ACS-2 (minor revision not indicated)
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 3.0 Gb/s)
Local Time is:    Thu Jul 14 12:10:33 2022 CEST
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:  (0x82) Offline data collection activity
          was completed without error.
          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 Offline
data collection: (52320) seconds.
Offline data collection
capabilities:     (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 routine
recommended polling time:        (   2) minutes.
Extended self-test routine
recommended polling time:        ( 523) minutes.
Conveyance self-test routine
recommended polling time:        (   5) minutes.
SCT capabilities:              (0x7035) SCT Status supported.
          SCT Feature Control supported.
          SCT Data Table supported.

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     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   196   187   021    Pre-fail  Always       -       7183
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       36
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   055   054   000    Old_age   Always       -       33525
 10 Spin_Retry_Count        0x0032   100   253   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   253   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       36
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       28
193 Load_Cycle_Count        0x0032   001   001   000    Old_age   Always       -       7866202
194 Temperature_Celsius     0x0022   113   103   000    Old_age   Always       -       39
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
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   200   200   000    Old_age   Offline      -       1

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%         8         -

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.

Nothing more to do than to reboot.

After reboot

The storage array was still not mounted, smartctl could now find /dev/sda:

[root@BUFFALO-4 ~]# df -h
Filesystem Size      Used Available Use% Mounted on
udev      10.0M         0     10.0M   0% /dev
/dev/md1   4.7G    766.8M      3.7G  17% /
tmpfs    121.1M     84.0K    121.0M   0% /tmp
/dev/ram1 15.0M    100.0K     14.9M   1% /mnt/ram
/dev/md0 968.7M    216.4M    752.2M  22% /boot

[root@BUFFALO-4 ~]# smartctl --all /dev/sda
smartctl 6.3 2014-07-26 r3976 [armv7l-linux-3.3.4] (local build)
Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Caviar Green (AF, SATA 6Gb/s)
Device Model:     WDC WD40EZRX-22SPEB0
Serial Number:    WD-WCC4E1XUDU4T
LU WWN Device Id: 5 0014ee 20cbde2d7
Firmware Version: 80.00A80
User Capacity:    4,000,787,030,016 bytes [4.00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Rotation Rate:    5400 rpm
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ACS-2 (minor revision not indicated)
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 3.0 Gb/s)
Local Time is:    Thu Jul 14 12:13:56 2022 CEST
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:  (0x84) Offline data collection activity
          was suspended 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 Offline
data collection: (52560) seconds.
Offline data collection
capabilities:     (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 routine
recommended polling time:        (   2) minutes.
Extended self-test routine
recommended polling time:        ( 526) minutes.
Conveyance self-test routine
recommended polling time:        (   5) minutes.
SCT capabilities:              (0x7035) SCT Status supported.
          SCT Feature Control supported.
          SCT Data Table supported.

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     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   250   204   021    Pre-fail  Always       -       4500
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       38
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   053   051   000    Old_age   Always       -       34713
 10 Spin_Retry_Count        0x0032   100   253   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   253   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       38
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       30
193 Load_Cycle_Count        0x0032   001   001   000    Old_age   Always       -       7823449
194 Temperature_Celsius     0x0022   122   106   000    Old_age   Always       -       30
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       13
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       11
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       14

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%         8         -

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.

Partition table after reboot

Now when both disks are in place again, I ran the (correct) command to list the partitions on all drives:

[root@BUFFALO-4 ~]# parted -l /dev/sdb
Model: ATA WDC WD40EZRX-22S (scsi)
Disk /dev/sda: 4001GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name     Flags
 1      17.4kB  1024MB  1024MB  ext3         primary
 2      1024MB  6144MB  5119MBprimary
 3      6144MB  6144MB  394kB primary  bios_grub
 4      6144MB  6144MB  512B  primary
 5      6144MB  7168MB  1024MBprimary
 6      7168MB  3992GB  3985GBprimary


Model: ATA WDC WD40EZRX-22S (scsi)
Disk /dev/sdb: 4001GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name     Flags
 1      17.4kB  1024MB  1024MB  ext3         primary
 2      1024MB  6144MB  5119MBprimary
 3      6144MB  6144MB  394kB primary  bios_grub
 4      6144MB  6144MB  512B  primary
 5      6144MB  7168MB  1024MBprimary
 6      7168MB  3992GB  3985GBprimary

...

Looks ok, so I tried mounting /dev/md10:

root@BUFFALO-4 ~]# mount /dev/md10 /mnt/array1/
[root@BUFFALO-4 ~]# df -h
Filesystem Size      Used Available Use% Mounted on
udev      10.0M         0     10.0M   0% /dev
/dev/md1   4.7G    766.8M      3.7G  17% /
tmpfs    121.1M     84.0K    121.0M   0% /tmp
/dev/ram1 15.0M    100.0K     14.9M   1% /mnt/ram
/dev/md0 968.7M    216.4M    752.2M  22% /boot
/dev/md10  7.2T      5.7T      1.6T  79% /mnt/array1
[root@BUFFALO-4 ~]# ls /mnt/array1/
backup/         buffalo_fix.sh* share/          spool/
[root@BUFFALO-4 ~]# ls /mnt/array1/share/
acp_commander/    buff4_public.txt  buff4_share.txt   buff4_web.txt

Checking the file system for errors

As I was able to mount the partition, I did a file system check after unmounting it:

[root@BUFFALO-4 ~]# xfs_repair /dev/md10
Phase 1 - find and verify superblock...
Not enough RAM available for repair to enable prefetching.
This will be _slow_.
You need at least 1227MB RAM to run with prefetching enabled.
Phase 2 - using internal log
        - zero log...
        - scan filesystem freespace and inode maps...
        - found root inode chunk
Phase 3 - for each AG...
        - scan and clear agi unlinked lists...
        - process known inodes and perform inode discovery...
        - agno = 0
        - agno = 1
...
        - agno = 30
        - agno = 31
        - process newly discovered inodes...
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 1
...
        - agno = 30
        - agno = 31
Phase 5 - rebuild AG headers and trees...
        - reset superblock...
Phase 6 - check inode connectivity...
        - resetting contents of realtime bitmap and summary inodes
        - traversing filesystem ...
doubling cache size to 1024
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify and correct link counts...
done
[root@BUFFALO-4 ~]# mount /dev/md10 /mnt/array1
[root@BUFFALO-4 ~]# ls /mnt/array1/
backup/         buffalo_fix.sh* share/          spool/

Another reboot, then checking to find out that md10 was still not mounted.
The error in NAS Navigator is: “E14:RAID array 1 could not be mounted. (2022/07/14 12:36:18)”

Time to check ‘dmesg’ again:

md/raid1:md2: active with 1 out of 2 mirrors
md2: detected capacity change from 0 to 1023410176
md: md1 stopped.
md: bind
md/raid1:md1: active with 1 out of 2 mirrors
md1: detected capacity change from 0 to 5114888192
md: md0 stopped.
md: bind
md/raid1:md0: active with 1 out of 2 mirrors
md0: detected capacity change from 0 to 1023868928
 md0: unknown partition table
kjournald starting.  Commit interval 5 seconds
EXT3-fs (md0): using internal journal
EXT3-fs (md0): mounted filesystem with writeback data mode
 md1: unknown partition table
kjournald starting.  Commit interval 5 seconds
EXT3-fs (md1): using internal journal
EXT3-fs (md1): mounted filesystem with writeback data mode
kjournald starting.  Commit interval 5 seconds
EXT3-fs (md1): using internal journal
EXT3-fs (md1): mounted filesystem with writeback data mode
 md2: unknown partition table
Adding 999420k swap on /dev/md2.  Priority:-1 extents:1 across:999420k
kjournald starting.  Commit interval 5 seconds
EXT3-fs (md0): using internal journal
EXT3-fs (md0): mounted filesystem with writeback data mode

The above shows that md0, md1 and md2 went up, but are missing its mirror partition (this from /dev/sda that disappeared).
Further down in dmesg output

md: md10 stopped.
md: bind
md: bind
md/raid0:md10: md_size is 15565748224 sectors.
md: RAID0 configuration for md10 - 1 zone
md: zone0=[sda6/sdb6]
      zone-offset=         0KB, device-offset=         0KB, size=7782874112KB

md10: detected capacity change from 0 to 7969663090688
 md10: unknown partition table
XFS (md10): Mounting Filesystem
XFS (md10): Ending clean mount
XFS (md10): Quotacheck needed: Please wait.
XFS (md10): Quotacheck: Done.
udevd[3963]: starting version 174
md: cannot remove active disk sda6 from md10 ...
[root@BUFFALO-4 ~]# mount /dev/md10 /mnt/array1/
[root@BUFFALO-4 ~]# ls -l /mnt/array1/
total 4
drwxrwxrwx    3 root     root            21 Dec 14  2019 backup/
-rwx------    1 root     root           571 Oct 14  2018 buffalo_fix.sh*
drwxrwxrwx    3 root     root            91 Sep 16  2019 share/
drwxr-xr-x    2 root     root             6 Oct 21  2016 spool/

What the h… “cannot remove active disk sda6 from md10”

Checking md raid status

[root@BUFFALO-4 ~]# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md10 : active raid0 sda6[0] sdb6[1]
      7782874112 blocks super 1.2 512k chunks

md0 : active raid1 sdb1[1]
      999872 blocks [2/1] [_U]

md1 : active raid1 sdb2[1]
      4995008 blocks super 1.2 [2/1] [_U]

md2 : active raid1 sdb5[1]
      999424 blocks super 1.2 [2/1] [_U]

unused devices: 
[root@BUFFALO-4 ~]# mdadm --detail /dev/md10
/dev/md10:
        Version : 1.2
  Creation Time : Fri Oct 21 15:58:46 2016
     Raid Level : raid0
     Array Size : 7782874112 (7422.33 GiB 7969.66 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Fri Oct 21 15:58:46 2016
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 512K

           Name : LS220D896:10
           UUID : 5ed0c596:60b32df6:9ac4cd3a:59c3ddbc
         Events : 0

    Number   Major   Minor   RaidDevice State
       0       8        6        0      active sync   /dev/sda6
       1       8       22        1      active sync   /dev/sdb6

So here, md10 is fully working and md0, md1 and md2 are missing their second device. Simple to correct, just adding them back:

[root@BUFFALO-4 ~]# mdadm --manage /dev/md0 --add /dev/sda1
mdadm: added /dev/sda1
[root@BUFFALO-4 ~]# mdadm --manage /dev/md1 --add /dev/sda2
mdadm: added /dev/sda2
[root@BUFFALO-4 ~]# mdadm --manage /dev/md2 --add /dev/sda5
mdadm: added /dev/sda5
[root@BUFFALO-4 ~]# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md10 : active raid0 sda6[0] sdb6[1]
      7782874112 blocks super 1.2 512k chunks

md0 : active raid1 sda1[0] sdb1[1]
      999872 blocks [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      4995008 blocks super 1.2 [2/1] [_U]
      [====>................]  recovery = 24.2% (1212672/4995008) finish=1.2min speed=48506K/sec

md2 : active raid1 sda5[2] sdb5[1]
      999424 blocks super 1.2 [2/1] [_U]
        resync=DELAYED

unused devices: 

Some time later, sync was finished, and I rebooted again. Finally, after this reboot /dev/md10 is automatically mounted to /mnt/array1 again.

Problem solved 🙂

smartctl notes

The values of attributes 5, 197 and 198 should be zero for a healthy drive, so one disk in the NAS is actually failing, but the cause of the hiccup (disconnect) was a core dump by smatctl weekly scan.

  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       13
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      11

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