There are many reasons to buy external hard drives, but the two primary reasons are: increased space (especially for media) and backups. However, the things needed when buying these external hard drives for these dissimilar situations mean that the principles needed to keep in mind when buying them are radically different. This is because different strengths are necessary for different goals.
When buying a hard drive for backup, cost, reliability, and portability are the most important factors. When buying a hard drive for media, size, speed, and ability to stow the hard drive away on your desk are more critical.
There are not any hard drives that meet all of these goals, unfortunately. However, there are some hard drives that are better for these types of tasks than others are. Picking the right tool for the right job is key to understanding the type of hard drive you need.
When buying a hard drive for backup, considering getting an unenclosed drive. While you will need to buy a hard drive bay to read the drives, unenclosed drives are *much* cheaper, in the long run, than enclosed ones are. Unfortunately, these drives require some technical know how in order to set them up and use them. Additionally, you need to buy a bay in which to load the backup drives.
One benefit to buying an unenclosed drive when buying a backup drive is that you can buy them in bulk. If you buy three, four, or five hard drives at a time, you can simply rotate them out when you need to use a new one.
As media increases in size, and consumers are getting larger media libraries, it is increasingly common to store *terabytes* of data (1,024 GB) simply for media such as music, movies, and e-books. The best way to store such large libraries is via external hard drives.
Since cost is not as large of a factor when buying media libraries -- since you will not be changing them out nearly as often -- you can take liberties when buying them. Look for a 1TB or 2TB external hard drive with good I/O speed for transferring data.
If you can find a hard drive that supports Thunderbolt or Firewire I/O, consider that. This is particularly true if you have a computer that supports thunderbolt or firewire, as these can have much faster I/O speeds than USB 2.0 (although USB 3.0 will, ostensibly, be much faster than USB 2.0 is).
Keep in mind that all hard drives eventually fail -- they are incredibly fragile. So, even if you are not accessing your data very often, as is often the case for a home media library hard drive, take care to make ample backups as often as possible. This is especially true for home media libraries, as they can be incredibly valuable — either monetarily or sentimentally.
Do not cut too many corners on cost. An expensive hard drive may seem like an unnecessary expense, but the difference between a relatively expensive hard drive and an inexpensive hard drive is *enormous*.