# watch -n1 cat /proc/mdstat

Sample outout:

Every 1.0s: cat /proc/mdstat                                                        Fri Apr 10 11:16:58 2015
 
Personalities : [raid10]
md0 : active raid10 sdf1[5] sdj1[9] sdg1[6] sdd1[3] sdi1[8] sdh1[7] sde1[4] sdb1[1] sda1[0] sdc1[2]
      19534428160 blocks super 1.2 512K chunks 2 near-copies [10/10] [UUUUUUUUUU]
      [===========>.........]  resync = 59.0% (11528658368/19534428160) finish=233.7min speed=570851K/sec
      bitmap: 61/146 pages [244KB], 65536KB chunk
 
unused devices: <none>

# watch -n1 iostat -k 1 2

Sample outout:

Every 1.0s: iostat -k 1 2                                                           Fri Apr 10 11:17:31 2015
 
Linux 2.6.32-431.23.3.el6.x86_64 (some.fqdn.com)        04/10/2015      _x86_64_        (4 CPU)
 
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          20.34    0.16    6.67    1.74    0.00   71.08
 
Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sdk               1.95        18.72       239.81    1631715   20901329
sdf             150.18     26406.77     16290.58 2301564614 1419856127
sde             186.58     27197.66      3230.58 2370496639  281571519
sdi             189.90     27195.76      3226.94 2370331546  281254427
sdc             187.29     27196.30      3227.99 2370378009  281345479
sdd             177.64     26408.21     16293.83 2301689934 1420139335
sdj             173.33     26408.48     16292.64 2301713769 1420035675
sda             189.55     27196.97      3228.75 2370436486  281412039
sdg             189.33     27195.72      3229.31 2370327509  281460979
sdb             172.44     26408.37     16294.25 2301704308 1420175943
sdh             177.32     26408.63     16294.97 2301726191 1420238643
md0             169.28      4691.05     16121.01  408863356 1405077288
 
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00   23.02    0.00    0.00   76.98
 
Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sdk               0.00         0.00         0.00          0          0
sdf             210.00    107520.00         0.00     107520          0
sde            1388.00    114176.00         0.00     114176          0
sdi            1345.00    113792.00         0.00     113792          0
sdc            1516.00    114176.00         0.00     114176          0
sdd            1516.00    114112.00         0.00     114112          0
sdj            1342.00    113792.00         0.00     113792          0
sda            1414.00    113792.00         0.00     113792          0
sdg            1572.00    114176.00         0.00     114176          0
sdb             237.00    121344.00         0.00     121344          0
sdh            1517.00    114176.00        64.00     114176         64
md0               0.00         0.00         0.00          0          0
 
 
 
 
# watch -n5 mdadm --detail /dev/md0
Sample outout:
Every 5.0s: mdadm --detail /dev/md0                                               Mon Apr 25 12:36:56 2016
 
 
/dev/md0:
        Version : 1.2
  Creation Time : Wed Apr 20 16:22:45 2016
     Raid Level : raid10
     Array Size : 15627540480 (14903.58 GiB 16002.60 GB)
  Used Dev Size : 3906885120 (3725.90 GiB 4000.65 GB)
   Raid Devices : 8
  Total Devices : 10
    Persistence : Superblock is persistent
 
  Intent Bitmap : Internal
 
    Update Time : Mon Apr 25 12:19:17 2016
          State : clean
 Active Devices : 8
Working Devices : 10
 Failed Devices : 0
  Spare Devices : 2
 
         Layout : near=2
     Chunk Size : 512K
 
           Name : mach217:0
           UUID : f5fd53a3:caedf390:08aba2ec:afd02b59
         Events : 148
 
    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1
       2       8       49        2      active sync   /dev/sdd1
       8       8       81        3      active sync   /dev/sdf1
       4       8       97        4      active sync   /dev/sdg1
       5       8      113        5      active sync   /dev/sdh1
       6       8      129        6      active sync   /dev/sdi1
       7       8      145        7      active sync   /dev/sdj1
 
       9       8      161        -      spare   /dev/sdk1
      10       8       65        -      spare   /dev/sde1
 
Find out which device, eg /dev/sdk, is which physical diskdrive
# smartctl -d sat -a /dev/sdk
 
Sample output:
smartctl 6.2 2013-07-26 r3841 [x86_64-linux-4.2.0-35-generic] (local build)
Copyright (C) 2002-13, Bruce Allen, Christian Franke, www.smartmontools.org
 
=== START OF INFORMATION SECTION ===
Device Model:     WDC WD40PURX-64GVNY0
Serial Number:    WD-WCC4E5NT0K77 <<<--------------- Find the harddrive with this serial!
LU WWN Device Id: 5 0014ee 2626fd6b1
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:        Not in smartctl database [for details use: -P showall]
ATA Version is:   ACS-2 (minor revision not indicated)
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Mon Apr 25 12:39:37 2016 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:  (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:  (49980) 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:  ( 500) minutes.
Conveyance self-test routine
recommended polling time:  (   5) minutes.
SCT capabilities:        (0x703d) SCT Status supported.
SCT Error Recovery Control 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   100   253   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   100   253   021    Pre-fail  Always       -       0
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       3
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   100   253   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       2
 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       -       3
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       1
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   Always       -       1
194 Temperature_Celsius     0x0022   116   114   000    Old_age   Always       -       36
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   100   253   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   100   253   000    Old_age   Offline      -       0
 
SMART Error Log Version: 1
No Errors Logged
 
SMART Self-test log structure revision number 1
No self-tests have been logged.  [To run self-tests, use: smartctl -t]
 
 
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.