Many years ago, I built an external hard drive by getting a Rosewill external hard drive enclosure, along with a 640GB Western Digital hard drive to go inside it. Combined, they gave me an external hard drive to use for monthly backups (in addition to the real-time cloud backups I get with CrashPlan).
Over time, the amount of data I have has grown immensely, especially since having children and starting to take more photos and videos. So, the 640GB, which seemed huge at the time, has become very tight as a backup destination.
So, I decided to upgrade the hard drive, keeping the Rosewill enclosure since it’s worked well over the years. I decided on a 2TB Toshiba hard drive. 2TB matches my primary data drive at the moment, and gives me a good amount of breathing room before I should need to upgrade either the primary drive or this backup drive, since my data amounts to just about 600GB.