External Hard Drive Basics

Backup storage options

The high-capacity external hard drives covered in this report are primarily intended for backup. They can also provide long-term external storage for multimedia files, such as digital video, high-resolution photos or music collections that occupy considerable hard drive space on a computer. Although you'll sacrifice performance with most external hard drives, they can provide a convenient way to increase your storage space with the added benefit that the drive may be unplugged and connected to another computer.

We found the most comprehensive and thorough review source to be ExtremeTech.com. Products are compared head-to-head, benchmark testing is exhaustive and ratings provide meaningful distinctions between hard drives. Tom's Hardware and England's Register Hardware and are also prolific reviewers of external hard drives, but each reviewer has different strengths. Register Hardware is extraordinarily objective while Tom's Hardware compares related products in roundup reviews and shows the most comparisons in benchmark tests. X-bit Labs is just as good at testing and reporting, but doesn't rate hard drives.

External hard drives have nearly unlimited storage capacity and modest per-gigabyte (GB) costs. Other external storage options include USB flash drives, which are faster and have the best portability, but capacity is currently capped at 64 GB; furthermore, the cost per gigabyte is much higher and security is lower. See our companion report on USB flash drives if one or several flash drives will be enough for your storage needs. Solid state drives -- which are fast and relatively free from mechanical failure -- are hitting the market now, but per-gigabyte prices put them out of range of most consumers.

Measured data transfer rates and speed are almost always the major factors in reviewer ratings. It is a big deal if you will actively use the drive, but it might not matter at all if the drive is just for backups. Reviewers also consider methods of connectivity (USB, FireWire, eSATA), ease of use, bundled or pre-installed software and physical design features, such as whether the drive sits vertically or horizontally (or can be used in either position).

Reviewers agree that backup software makes a difference in the utility of these drives. Nearly all moderately priced to expensive external hard drives come with software to help schedule backups and move files, and features include system rollback capability as well as security options that keep your drive safe from sudden disconnects, shutdowns and virus invasions (a risk for drives that are switched among multiple computers). You don't need to use the manufacturer's supplied software with an external hard drive. You can drag and drop files, bypassing software entirely, or use third-party software. Budget hard drives rarely include backup software, but they are also rarely reviewed.

For the most part, the reviews we found say that the majority of external hard drives do exactly what they are supposed to do. Professional reviews are almost uniformly good across the board. However, user reviews occasionally tell another story. Newegg.com, Amazon.com and CNet.com's user reviews all have entries by frustrated owners who recount their hard drive disasters.

Experts at Tom's Hardware state unequivocally that all hard drives will eventually fail, whether it's an internal hard drive inside your computer or an external hard drive. If you are storing critical, irreplaceable data on an external hard drive, experts recommend creating two backups. Storing identical data on two different drives virtually eliminates the chance that you could lose all your data following a drive failure. You can use internal or external drives in a RAID array to create redundant backups, or you can use any combination of backup methods. Storing a few DVDs away from your computer can preserve your most valuable work if your computer equipment is stolen or lost in the event of fire.

Just as the hard drive inside your computer could falter at virtually any point, the same goes for an external hard drive. An external hard drive should most definitely be part of a larger backup and storage plan -- not your only repository for important, irreplaceable data files, photos, video or other information.

According to reviews, some hard drives are quiet in operation, but others generate noise that can be as annoying as a commercial jingle you can't clear from your head. Heat and reliability are closely related, and any electronic product that runs too hot can be a failure waiting to happen. Several factors can be used to gauge reliability: brand history and reputation, user reviews, the manufacturer's limited warranty for a specific drive and the manufacturer's MTBF specification (not all manufacturers publish one).

MTBF stands for "mean time between failures." It tells you how long (in hours) an average unit will last. A Carnegie Mellon University study conducted last year found that MTBF estimates are grossly exaggerated. The worst drives failed 15 times sooner than projected. Therefore, you can't believe an individual MTBF figure, but the differences in MTBF figures can be meaningful. Experts still recommend redundant backups of key data.