[Up front disclosure : My company manufactures a storage product].
Carl : 1 drive per month out of 700 drives is an AFR (Annualised Failure Rate) of about 1.7%, which pretty much concurs with the Backblaze analysis, and I'm sure your systems have the same high-quality conditions that they will have in their data centres.
The key to long hard drive life is mentioned several times in the articles and discussions above, by referring to "the right conditions", but that doesn't just mean in controlled data centre conditions. There are three key factors which affect expected hard drive life : Temperature; Vibration; Wear.
If you reduce the operating temperatures, minimise or eliminate vibration (from other disks, from fans etc.) and minimise the duty cycle (wear rate) of the disks, then the disk lifetimes will increase considerably. I recently spent time at Seagate HQ discussing these factors with some key people and they confirmed exactly these points. Conversely, if you run the disks hot, have them in a high-vibration environment, and use them at 100% duty cycle, then their useful lifetime will be considerably shorter.
For surveillance applications specifically, there are ways in which to dramatically increase the reliability and lifetime of disks and at the same time reduce power consumption and maintenance costs, using non-RAID approaches, which involve reducing the operating temperatures (by not heating the drives up in the first place), eliminating vibration using a sequential filing system and very low power fans (or no fans) and also by switching drives off when they are not needed. These techniques are also highly suited to ever-increasing disk capacities and long retention times.
I don't want to be accused of plugging a specific product, so suffice to say that alternative approaches exist for surveillance which can deliver very long disk lifetimes with very low failure rates (less than 0.1% AFR).
