mdadm is a command line tool to manage Software Raid in Linux. To see stats of Raid, run

root@server46 [~]# mdadm --misc --detail /dev/md3
/dev/md3:
        Version : 0.90
  Creation Time : Thu Nov 26 02:42:44 2015
     Raid Level : raid1
     Array Size : 1795814336 (1712.62 GiB 1838.91 GB)
  Used Dev Size : 1795814336 (1712.62 GiB 1838.91 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 3
    Persistence : Superblock is persistent

    Update Time : Wed Dec  2 04:33:43 2015
          State : clean 
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           UUID : 66e02f1f:de10d989:a4d2adc2:26fd5302
         Events : 0.71

    Number   Major   Minor   RaidDevice State
       0       8        3        0      active sync   /dev/sda3
       1       8       19        1      active sync   /dev/sdb3
root@server46 [~]#