wíth RAID, beware of the problem of losing the RAID controller card (i.e., the hardware which controls the data in the hard disks). Two different model RAID adapters are not necessarily compatible in the way they split data between drives.
In the case you crash an old card, you may have a hard job of finding identical card to read your drives.
RAID 1 is easier on this as it simply duplicates everything. The advantage is that the PC may read simulataneously from two disks, thus speeding up all reading operations. However, having two disks inside a PC (or whatever box) is a risk as the whole packet may burn down or suffer from a power failure (e.g., due to electric current frequency fluctuation).