External hard drives are extremely useful for backing up or archiving large amounts of data, and they can be purchased at many major retailers including Best Buy, Staples, Walmart and of course online. They are a fairly commodity item that you can walk in and purchase, but there are a few things you should consider when selecting a specific model:
Don't spend more than $150 on a single external hard drive. Many good models can be had for less than $100.
Don’t buy the largest model out there. You can find drives in 1TB (1000GB), 500GB, 320GB, 250GB, etc, capacities, but for most offices 250GB will be more than adequate.
Get USB 3.0. This is how the drive connects to your computer. External drives come in a handful of connection types including USB 2.0 and eSATA. USB 3.0 will work on older computers that still have USB 2.0 drives and will offer faster write speeds when connected to a USB 3.0 port. eSATA, while offering improved write speeds, is not a common port on computers. USB 3.0 ports are standard on most any current computer.
Don’t keep all your eggs in one basket. Backing up to an external drive and keeping the original on a file server share or your local computer protects you if one copy is lost. However, archiving to a single location (by deleting the original copy) can put you at risk if the archive is lost. For added protection purchase a second external hard drive or upload your files to CyBox. Also don't forget to store the backup and original or two archive copies in different locations. Floods, fire, theft and lightning all happen.