Reliability & Other Factors
Performance isn't everything. The hard drive stores our data, which is arguably the most important thing in our PC. That includes our documents, photos, videos - basically our entire computing experience. Losing all that data would be similar to wiping out your history and memory... forcing you to start afresh. It's no fun at all. So, hard drive reliability should always be a critical factor.
Bearings – Drives have bearings that the main platters sit on. Bearings allow the platters to spin with minimal friction, noise and heat. Hard drives generally use either one of two types of bearings - the traditional multi-ball bearing or the newer fluid dynamic bearing. Ball bearings are noisier and more prone to damage and wear than fluid dynamic bearings. However, they are far cheaper and this keeps them in production. Fluid dynamic bearings allow for quieter and more reliable operation by floating the spindle in an assembly which is totally sealed from the outside. This makes problems like lubricant evaporation, bearing wear and heat warping things of the past. So, if you want a quieter and more reliable hard drive, get one with a fluid dynamic bearing.
Shock Tolerance – Rated in G, it denotes the amount of shock a hard drive can withstand. Manufacturers usually provide two numbers - operating shock and non-operating shock. A high shock tolerance is always better, especially if you intend to use the drive in a mobile capacity. Do not assume that only operating shock is of any importance. Surveys have shown that that most damage that affect a hard drive's long-term reliability actually occur during transportation.
Power Consumption – Not a reliability metric per se. Hard drives that consume less power will produce less heat. That indirectly improves its reliability although the actual quantum cannot be determined. Needless to say, reducing power consumption will help reduce our electricity bills. In mobile applications, a lower power consumption also means a longer battery life.
Dampening Technologies – It has been a long time since hard drive dampening technology (like Seagate's SeaShield) debuted. There's not really much to it though. Dampening usually comes in the form of the hard drive's case being padded with dense foam and its internal components dampened with soft grommets. Do not confuse this with accelerometer-based active hard drive protection technologies since dampening is a passive method.
Noise levels – Measured in Bels or deciBels, it is the measure of a hard drive's Sound Pressure Level (SPL), or basically how noisy it can get. Most numbers are quoted in deciBels (dB), but if you see numbers quoted in Bels, just multiply it by 10 and you have the number in deciBels (dB). Anything around 20-30 dB is generally silent, but that is up to you to judge because the perception of noise very much differs from one person to another.
Vibration – Vibration is essentially noise outside the audible level, at the very low frequency of 500 Hertz or less. Although most users do not need to bother about this, those using light aluminium cases will need to be careful as the case will not be able to damp out the vibration. The metric for vibration is Rads. Always look for a hard drive that has a higher vibration tolerance.
MTBF – Short for Mean Time Before Failure, it is a pretty ambiguous and questionable estimate of how long a hard drive can be expected to work before failing under normal usage patterns. These estimates are obtained by subjecting large numbers of random hard drive samples to extreme conditions to acceleration deterioration. For example, they are subjected to higher heat levels to accelerate the effects of aging. The number of failures are analyzed to generate the MTBF figure. However, the different methods of testing by each manufacturer makes it hard to determine which hard drive is truly more reliable.
AFR – Short for Annualized Failure Rate, it is similar to MTBF except that it is given as a percentage of the probability that the hard drive will fail during operation. A figure of 0.6 % would mean that the hard drive has a 0.6 % chance of failure in a year.
Warranty – I usually don't talk about this for most computer components, but when it comes to the hard drive, a long warranty is always a good thing to look for. It is not only an indication of how confident the manufacturer is of the reliability of their product, it also reduces the pain of losing a hard drive. However, instead of just looking for the longest warranty available, be sure to check the policy too. Take your time to read through what the manufacturer defines as a defect that is covered by the warranty. Some hard drive manufacturers refuse to accept any hard drive with S.M.A.R.T. scores that were below a certain limit. So, be sure to check what the manufacturer of your hard drive determines is acceptable for RMA (Return Materials Authority).