> ...if you turned it on about 3 times a day on average,
> the drive might last for approx three years.
I don't know whether it was the source or your math, but you are off by a factor of over 10... 3 times a day for 3 years is only 3,285 cycles and manufacturers rate 3.5" drives for 50,000 start/stop cycles. That doesn't mean an HDD won't fail before then as explained by the reference at http://www.economicexpert.com/a/Hard:disk.htm
"The sliders (the part of the head that is closest to the disk and contains the pickup coil itself) are designed to reliably survive a number of landings and takeoffs from the disk surface, though wear and tear on these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear - when a drive is younger and has fewer start/stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage drive (literally, as the head drags along the drive surface until the air bearing is established). For the Maxtor DiamondMax series of drives, for instance, the drive typically has a 0.02% chance of failing after 4,500 cycles, a 0.05% chance after 7,500 cycles, with the chance of failure rising geometrically to 50% after 50,000 cycles, and increasing ever after."
According to this, your 2160 will still have a 99.99% chance of working after turning it on/off 3 times/day for 3 years.
Most of us would be happy with those odds, but if you are still seriously worried then replace your 3.5" with a 2.5" PATA 160GB or 320GB drive because the 2.5" are designed for notebooks which are constantly cycling up/down and have a higher landing/takeoff specification.
You do need to avoid doing things that maximize the likelihood of failure e.g. putting your DVR in an unventilated cabinet so that it operates at high ambient temperatures or powering off, changing your mind, and powering on again. The worst period of head instability is during takeoff and landing, and interrupting the landing by powering back on could cause a head crash: wait at least 15 seconds, preferably 30.
Most drive failures are not related to takeoff/landing issues, and since the typical warranty period on drives is 3 years then you can interpret that to mean "at least three years", because that's the period a manufacturers expects no returns related to age (most warranty claims occur in the first 90 days). Some drives are still warranted for five years see http://support.wdc.com/warranty/poli...pe=res&lang=en