fatal error -- Input/output error
This is almost for sure a hardware error. Try a diagnostic tool from the disk vendor.
I can't access the 2 which is labeled Linux Raid Member.
Although I remeber I set up the NSA210 under JBOD system, why is now under Raid?
The data partition on a ZyXEL is always a raid array. In your case probably a single disk raid1 array.
and how can I have access to this Raid?
By assembling it. Open a terminal, and find out the device node of the data partition:
It's probably sdb2. The size is given in 'blocks', which are kB.
When you have located the partition, assemble the array:
sudo mdadm --assemble /dev/md0 /dev/sdb2 --run
When this succeeds, you can try to mount /dev/md0. (Which will possibly fail due to that filesystem error).
Maybe you have to install mdadm first:
sudo apt-get update
sudo apt-get install mdadm --no-install-recommends