Thanks again for the help. I am struggling a bit with the intricacies of this but am progressing a little I think. I have not yet tried Russell's suggestion of purchasing two new 4TB drives because of the expense but will go in that direction as a last resort. I have copied the data onto 2TB drives which are the same size and type as the originals. Not sure if that will achieve all that is required. I have been trying with mdadm to mount the drive but so far with no success. My mdadm.conf shows the drive: # definitions of existing MD arrays ARRAY /dev/md/2  metadata=1.2 UUID=b5f4346d:deb6f751:e69ac550:b0b961fe name=DiskStation:2 but when I try to mount the partition sda5 I get: bob@Comp1:~$ sudo mount /dev/md2 /media/ntfs mount: /media/ntfs: can't read superblock on /dev/md2. bob@Comp1:~$ cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md2 : inactive sda5[0](S)       1948779840 blocks super 1.2 unused devices: <none> Any further instructions or suggestions appreciated Bob