Any Linux PC can do. Any PC booted from a Linux Live CD or -USB stick is sufficient.
Connect one disk to your Linux PC, and open a console (terminal). Locate your disk:
You will see disks (sdx
where x = [a..z]) and partitions (sdxn
where n = [1..]). The size is given in blocks, which are kB. ZyXEL puts the data partition on the 2nd partition, So you are searching for a sdx
2, which is about 3000000000 blocks.
In the rest of the story I'll assume the datapartition to be sdb2
Now type 'su' or 'sudo su' (depending on your distro) to get root access. Assemble the raid array from one disk:
mdadm --assemble /dev/md0 /dev/sdb2 --run
Create a mountpoint and mount it:
mkdir -p /tmp/mountpoint
mount -o ro /dev/md0 /tmp/mountpoint
Now you can access your data via the gui in /tmp/mountpoint.
Raid is not a backup. It protects you against failure of a single disk, but doesn't protect you against all other threats. A good backup is offline, and preferably offsite.