Suddenly my Raid ist not available

Version : 1.2
  Creation Time : Mon Nov  4 20:05:16 2013
     Raid Level : raid5
     Array Size : 8790795264 (8383.56 GiB 9001.77 GB)
  Used Dev Size : 2930265088 (2794.52 GiB 3000.59 GB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent


    Update Time : Tue Dec 24 22:11:05 2013
          State : clean
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0


         Layout : left-symmetric
     Chunk Size : 512K


           Name : openmediavault:Volume  (local to host openmediavault)
           UUID : b96a03c0:a426bac9:1bec6f04:67fdbd65
         Events : 92


    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb
       2       8       48        2      active sync   /dev/sdd
       3       8       64        3      active sync   /dev/sde

root@openmediavault:~# mount -a
root@openmediavault:~# mount
/dev/sdc1 on / type ext4 (rw,noatime,discard,errors=remount-ro)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
tmpfs on /tmp type tmpfs (rw)
fusectl on /sys/fs/fuse/connections type fusectl (rw)

root@openmediavault:~# cat /etc/fstab 
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    defaults        0       0
# / was on /dev/sda1 during installation
UUID=0ea57f9e-8f13-48ff-b6d0-4db6317c6241 /               ext4    noatime,discard,errors=remount-ro 0       1
# swap was on /dev/sda5 during installation
UUID=2e4ec378-56a4-46f7-8865-5495a54fcf4c none            swap    sw              0       0
/dev/sdb1       /media/usb0     auto    rw,user,noauto  0       0
tmpfs           /tmp            tmpfs   defaults        0       0
# >>> [openmediavault]
UUID=d52272e1-1234-4e3e-8330-1afc9a7ff4dc /media/d52272e1-1234-4e3e-8330-1afc9a7ff4dc ext4 defaults,nofail,acl,user_xattr,noexec,usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0 0 2
/media/d52272e1-1234-4e3e-8330-1afc9a7ff4dc/NAS/ /home/ftp/NAS none bind 0 0
# <<< [openmediavault]

root@openmediavault:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdc1              53G  4.3G   46G   9% /
tmpfs                 3.8G     0  3.8G   0% /lib/init/rw
udev                  3.8G  172K  3.8G   1% /dev
tmpfs                 3.8G     0  3.8G   0% /dev/shm
tmpfs                 3.8G  4.0K  3.8G   1% /tmp
root@openmediavault:~# 
root@openmediavault:~# 
root@openmediavault:~# blkid
/dev/sdc1: UUID="0ea57f9e-8f13-48ff-b6d0-4db6317c6241" TYPE="ext4" LABEL="SSD" 
/dev/sdc5: UUID="2e4ec378-56a4-46f7-8865-5495a54fcf4c" TYPE="swap" 
/dev/sda: UUID="b96a03c0-a426-bac9-1bec-6f0467fdbd65" LABEL="openmediavault:Volume" TYPE="linux_raid_member" 
/dev/sdb: UUID="b96a03c0-a426-bac9-1bec-6f0467fdbd65" LABEL="openmediavault:Volume" TYPE="linux_raid_member" 
/dev/sdd: UUID="b96a03c0-a426-bac9-1bec-6f0467fdbd65" LABEL="openmediavault:Volume" TYPE="linux_raid_member" 
/dev/sde: UUID="b96a03c0-a426-bac9-1bec-6f0467fdbd65" LABEL="openmediavault:Volume" TYPE="linux_raid_member"