Linux device disks

We were just checking a linux server  that currently has a 4 physical disk drives and one of them  failed. The following are outputs for the system.  We dont' know Linux. Could someone explain the outputs. Like for instance: what is md1 and are sdb3 and sda3  the physical disks or partitions of a physical disk.
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[root@r101s0u1bak ~]# cat /proc/mdstat
Personalities : [raid1] [raid0]
md5 : active raid0 md3[0] md4[1]
      3802994752 blocks 64k chunks

md1 : active raid1 sdb3[1] sda3[0]
      8008320 blocks [2/2] [UU]

md3 : active raid1 sdb5[1] sda5[0]
      1899493312 blocks [2/2] [UU]

md2 : active raid1 sdc1[1]
      50010176 blocks [2/1] [_U]

md4 : active raid1 sdc2[1]
      1903501568 blocks [2/1] [_U]

md0 : active raid1 sdb2[1] sda2[0]
      45761088 blocks [2/2] [UU]
----------------------------------------------------

[root@r101s0u1bak ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/md0               43G  4.0G   37G  10% /
/dev/md2               47G  625M   44G   2% /usr/bp
/dev/sdb1             236M   18M  206M   8% /mnt/boot_sync
/dev/sda1             236M   18M  206M   8% /boot
tmpfs                 3.9G     0  3.9G   0% /dev/shm
/dev/md5              3.6T  1.6T  2.0T  44% /backups
[root@r101s0u1bak ~]#
ShenAsked:
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ozoConnect With a Mentor Commented:
I would guess that md2 and md4 would normally have a mirror on /dev/sdd#, and that this is the drive that failed.
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ozoConnect With a Mentor Commented:
md5 : active raid0 md3[0] md4[1]
      3802994752 blocks 64k chunks
/dev/md5 is an active, raid0 array  with component devices  /dev/md3 [device 0] and /dev/md4 [device 1]

md1 : active raid1 sdb3[1] sda3[0]
      8008320 blocks [2/2] [UU]
/dev/md1 is an active, raid1 array with component devices /dev/sdb3 [device 1] and  /dev/sda3  [device 0]
out of 2 devices, 2 are in use, and both are Up

md3 : active raid1 sdb5[1] sda5[0]
      1899493312 blocks [2/2] [UU]
/dev/md3 is an active, raid1 array with component devices /dev/sdb5 [device 1] and  /dev/sda5  [device 0]
out of 2 devices, 2 are in use, and both are Up

md2 : active raid1 sdc1[1]
      50010176 blocks [2/1] [_U]
/dev/md2 is an active, raid1 array with component device /dev/sdc1 [device 1]
out of 2 devices, 1 is in in use, device 0 is down and device 1 is up

md4 : active raid1 sdc2[1]
      1903501568 blocks [2/1] [_U]
/dev/md4 is an active, raid1 array with component device /dev/sdc2 [device 1]
out of 2 devices, 1 is in in use, device 0 is down and device 1 is up

md0 : active raid1 sdb2[1] sda2[0]
      45761088 blocks [2/2] [UU]
/dev/md0 is an active, raid1 array with component devices /dev/sdb1 [device 1] and  /dev/sda2  [device 0]
out of 2 devices, 2 are in use, and both are Up

sdx# is partition # on scsi device x
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ShenAuthor Commented:
So if I undertand it:
   the raids  names are the dev/md0..4  
  and  dev/sdbx[] , dev/sdax[], dev/sdcx[], dev/mdx[] are partitions of sdb, sda,  sdc, md  physical devices since the machines has 4 physical drives?
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ShenAuthor Commented:
Please forget my previous response:

After reading your explanation more:

all the sdbx,sdax,sdcx, mdx are partitions in 2  devices [0] or [1]. Each devices (0,1) is raid 1, so this makes 4 physical drives.
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ShenAuthor Commented:
thanks.  Do you suggest any tools to fix the drive
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Saravanan PalanisamySystems EngineerCommented:
Use mdadm command utility to replace the failed drive.
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