When it comes to buying an external or internal hard drive for backup purposes, it doesn’t make sense to skimp. As a backup drive, this is where all your important data will be stored, possibly for a few years or more. Your backup drive is your last resort in case of disaster, which means it should be the safest place for your data, not the cheapest place. To understand some specifications that indicate a high quality, reliable hard disk drive, familiarize yourself with some of the terms below.
Mean Time Between Failures
Mean time between failures (MTBF) is a figure oft-cited by manufacturers, and for many consumers, it’s the sole indicator of reliability. MTBF is an aggregate analysis of how long a particular model of hard drive operates before random errors begin occurring. If the disk is new to the market, the manufacturer will get this number by running controlled tests on a large number of drives. This results in a theoretical MTBF. After a hard drive has been on the market for a while, the manufacturer can begin gauging how long they typically last in the real world. This data gives them an operational MTBF.
MTBF is only marginally useful. This is because MTBF gives you aggregate information about a large number of hard drives being tested, rather than information about a particular unit. Among the tested drives, there are likely those that last far longer than the operational MTBF and those that last much shorter than the operational MTBF. An MTBF is no guarantee that your drive will last a certain amount of time.
With hard disk drives, there is usually a bathtub curve of failure rates. Most drives that are destined to fail will do so within the first few days or weeks of use. Beyond that, most will remain reliable for a certain number of years before the chance of failure steadily begins to increase. The rated service life is the manufacturer’s assessment as to how long you can use your hard drive before that risk of failure begins to increase. This is usually a period of two to five years, and it basically says that if your hard drive has lasted that long, the it’s probably not a bad idea to start thinking about buying a new one. The failure won’t occur instantly after you’ve exceeded the estimated service life, but the chances of gradual failure begin to increase after that point.
Whereas the service life is how long the manufacturer expects a hard drive to function reliably, the warranty length is how long a manufacturer guarantees that it will work. If a hard drive fails within the warranty period, they will repair it or replace it. This warranty length usually gets you through that early failure rate on the aforementioned bathtub curve, which helps you avoid buying “lemons.”
Warranties can range from three years to five years or longer. More expensive drives typically come with longer warranties. Refurbished and cheaper drives may have warranties as short as 90 days or a year.
Hard drives including very small, very delicate moving parts. These parts are subject to wear and tear. The wear typically occurs when the hard drive is spinning up (start) or returning to idle (stop). Laptop hard drives will usually be subjected to more start/stop cycles during use, since idling the drives when not in use saves power.
When a manufacturer cites start/stop cycles in the specs, this is a rating of the minimum amount of start/stop cycles the drive should be able to handle within its service life. The higher the number, the better, but as with MTBF, this is no guarantee.
Although not typically included on the short tech specs sheet, detailed technical specifications may include an unrecoverable error rate. This is usually a very low rate, such as <1 in 1013 which means that errors occur less than once for every 100 trillion operations.
Among hard drives in the same class, error rates hardly vary. If you are trying to decide between two very similar drives, comparing error rates may be useful. But again, this is just another piece of data, like start/stop cycles and MTBF, and not a guarantee from the manufacturer about your particular unit.
The above terms may give you a better idea of how to vet a backup hard drive. But at the end of the day, getting a quality hard drive with a solid warranty from a reputable dealer is the key. Avoid buying used or refurbished hard drives from third party vendors, since these drives may not carry the same warranties offered by the manufacturer.
Choosing a Reliable Backup Hard Drive
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