I've found the 3Tb to be reliable, but NO external drive is reliable enough to trust as a sole backup. Use cloud backup to several sites for really important stuff. I just got a free 25Gb space to do key backups from BOX.COM and use it with several others in addition to local backup on externals and other devices.
bah.. cloud is too slow. go for a nas box with a couple of raid1 drives in it is what I recommend.
I have RAID arrays at home, but when the house fire comes they are completely useless for important data. RAID is not an alternative to good offsite backup, that's like day one stuff in data protection.