RAID 3 and onwards employ data stripping with data redundancy stored on all the drives, which is why it is difficult to recovery data once the array goes down. Unless the Buffalo Quad supports duplexing (2 seperate dedicated independent controllers) controlling the 2 drives, you will suffer also from a RAID 1 failure if the controller fails. Remember, in a RAID array, drive failure IS NOT the only fault. Controller and power supply failure can do that too. If the controller starts going, it will start writing corrupt data and if the power supply starts going, the voltage levels may not be within specs to ensure data writing or reading consistency either!
Again, if one can prevent RAID failures completely, why are DRS (Data Recovery Specialists) run a booming business?
Imagine RAID 5 as a gigantic single disk drive. If you want about 3Tb contagious storage, then your Quad provides that. But remember that the MTBF (Mean Time Between Failure) of each individual drives are reduced by 1/4 of their lifespan, NOT their quoted lifespan. For example, if a drive is rated for 100,000 hours and all 4 of them are identical, their true MTBF would be 25,000 hrs only. Since they all go on together, this means that if one of your RAID drive fails, what stops it from another drive to fail at the same time?!? RAID 1 failure do exist, which is why, the best solution for you is to purchase 2 individual 2TB external drives and then back your Quad up to them. When the Quad fails to reboot after you replaced its failed drive, you still have those backups you can restore from. From my experience dealing with these data failure issues, it is FASTER to recover from a RAID failure if you have either backups on external drive or better yet another Quad you can run with while the failed Quad gets serviced or replaced and then RSYNCed later on from the backup Quad.
Sorry to be the purveyor of bad news, but if you value your data much and you need RAID, this is what you will have to consider..