what your overlooking with respect to the hard drives is that when they fail its catastophic because much more data is lost than an isolated CD/DVD disk or file. If you go with hard drives you would have to use 2 to prevent this like you say. ...
Read the workflow description. I use hard drives in pairs for backup/ archiving. That makes THREE copies of currently used data (on the 'working', 'backup 1' and 'backup 2' drives). The chance of all three media failing simultaneously is infinitesimally small, particularly if at least one of them is disconnected from power and the computer system except when backups are being performed.
An advantage to working with paired hard drives is that if one goes bad, you just buy another bare drive, format it, and block copy the other one back to it. This can be done on a 250Gbyte volume MUCH MUCH more quickly than recovering from DVDs or CDs since the hard drive media is easily capable of 10x the data transfer speed. Try reading 200Gbyte of data from one set of backup DVDs to another. As a test, I transferred that quantity of data from one drive to another in about 65 minutes over a FireWire 400Mbps connection.
Secondly, if you have a nasty power supply failure or surge issue you CAN destroy all hard drives in the tower that share that power supply/chassis. HDDs are also vulerable to malicious viruses, OS bugs, etc. which burned media are not.
Each of my backup drives is in its own, external, separately connectible power enclosure. They are always powered through a spike protected power supply with emergency battery backup. The most common cause of hard drive failure is poor quality power supplies so don't skimp on the quality of power enclosures or the power supply to the systems if you want to be safe.
Your concerns about viruses and bugs are extremely valid for Windows systems but virtually unheard of for Linux or Mac OS X systems. Optical media, mastered from a buggy system, are just as good a carrier of Windows viruses as hard drives, particularly if you master DVDs or CDs with FAT or NTFS rather than the ISO standard file systems. I know of several cases where this is how viruses infiltrated entire companies.
.. I simply ASSUME the HDDs will fail ...
It's always a safe thing to assume that media will fail if want to keep data safe. Relying on *any* single archive of your data onto *any* media format is foolish. I said it before, and I repeat it for emphasis: "Multiple copies are the key to proper digital archiving." Individual media longevity is a far less important consideration than it is in the world of film and prints. Transfer speed, fast random access, and high capacity makes maintaining digital data efficient.
Godfrey
