My Raid 5 array (4 1tb Disks WD10EARS) had was showing as degraded. I looked and one of the disks wasnt installed, so i re-added it with the mdadm add command.

the array is now showing as (null)Array , but cant be mounted

if i run:

root@warren-P5K-E:/home/warren# sudo mdadm --misc --detail /dev/md0

I get:

mdadm: cannot open /dev/md0: No such file or directory

and running:

root@warren-P5K-E:/home/warren# cat /proc/mdstat 

gives me:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]

unused devices: < none >

The data is very important

root@warren-P5K-E:/home/warren# mdadm --examine /dev/sda
/dev/sda:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 00000000:00000000:00000000:00000000
  Creation Time : Sat May 26 12:08:14 2012
     Raid Level : -unknown-
   Raid Devices : 0
  Total Devices : 4
Preferred Minor : 0

    Update Time : Sat May 26 12:08:40 2012
          State : active
 Active Devices : 0
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 4
       Checksum : 82d5b792 - correct
         Events : 1


      Number   Major   Minor   RaidDevice State
this     1       8        0        1      spare   /dev/sda

   0     0       8       16        0      spare   /dev/sdb
   1     1       8        0        1      spare   /dev/sda
   2     2       8       32        2      spare   /dev/sdc
   3     3       8       48        3      spare   /dev/sdd

root@warren-P5K-E:/home/warren# mdadm --examine /dev/sdb
/dev/sdb:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 00000000:00000000:00000000:00000000
  Creation Time : Sat May 26 12:08:14 2012
     Raid Level : -unknown-
   Raid Devices : 0
  Total Devices : 4
Preferred Minor : 0

    Update Time : Sat May 26 12:08:40 2012
          State : active
 Active Devices : 0
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 4
       Checksum : 82d5b7a0 - correct
         Events : 1


      Number   Major   Minor   RaidDevice State
this     0       8       16        0      spare   /dev/sdb

   0     0       8       16        0      spare   /dev/sdb
   1     1       8        0        1      spare   /dev/sda
   2     2       8       32        2      spare   /dev/sdc
   3     3       8       48        3      spare   /dev/sdd
root@warren-P5K-E:/home/warren# 
oot@warren-P5K-E:/home/warren# mdadm --examine /dev/sdc
/dev/sdc:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 00000000:00000000:00000000:00000000
  Creation Time : Sat May 26 12:08:14 2012
     Raid Level : -unknown-
   Raid Devices : 0
  Total Devices : 4
Preferred Minor : 0

    Update Time : Sat May 26 12:08:40 2012
          State : active
 Active Devices : 0
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 4
       Checksum : 82d5b7b4 - correct
         Events : 1


      Number   Major   Minor   RaidDevice State
this     2       8       32        2      spare   /dev/sdc

   0     0       8       16        0      spare   /dev/sdb
   1     1       8        0        1      spare   /dev/sda
   2     2       8       32        2      spare   /dev/sdc
   3     3       8       48        3      spare   /dev/sdd
root@warren-P5K-E:/home/warren# mdadm --examine /dev/sdd
/dev/sdd:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 00000000:00000000:00000000:00000000
  Creation Time : Sat May 26 12:08:14 2012
     Raid Level : -unknown-
   Raid Devices : 0
  Total Devices : 4
Preferred Minor : 0

    Update Time : Sat May 26 12:08:40 2012
          State : active
 Active Devices : 0
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 4
       Checksum : 82d5b7c6 - correct
         Events : 1


      Number   Major   Minor   RaidDevice State
this     3       8       48        3      spare   /dev/sdd

   0     0       8       16        0      spare   /dev/sdb
   1     1       8        0        1      spare   /dev/sda
   2     2       8       32        2      spare   /dev/sdc
   3     3       8       48        3      spare   /dev/sdd

That on the 4 drives.