A 2TB external hard drive would be ample space for a backup drive or if it is added on to a computer to extend space. Depending on what you want to spend there are the standard HDDs or the newer Solid State Drives (SSD). The SSDs are faster as they don't have moving parts, thus speeding up the read and write times.

2TB is quite some space

It would take a while to fill up a 2TB external hard drive unless one does regular video editing work or an insane amount of photography in raw format. This kind of space could otherwise last one a decade of music, files and pictures. This would make for a great backup storage device separate from one's regular work hard drive, neat and organised in case it is ever needed. Backing up files is sensible as losing a computer hurts more due to the information loss and not as much due to the machine itself.

Portable convenience

Even at 2TBs an external hard drive is a very portable size nearly fitting in the palm of your hand, making it very easy to store in drawers or safes if you really want to keep your information safe physically as well.

Connectivity and speed

General connectivity is through a USB or FireWire, some have eSATA and others the option of WiFi. The wireless ones require an external power source as well to amp up the WiFi systems. It is quite convenient to have a short USB cable with a massive amount of storage at the other end with fast access. The speeds of transfer also vary depending on the connection in use, brand and what new technology is now available. What you pick depends on your need and budget of course.

Other considerations

There are even 2TB drives that have a shockproof case. If you end up dropping it by mistake, the inside won't crack and lose all it contains. Many brands make these kinds of drives in two different ways Solid State Drives (SSD) or the older HDDs. Without having any moving parts SSD is faster and more efficient when you want to access files as the drive uses electronic circuits to write and retrieve, based on the Flash Memory technology. Akin to RAM chips that are the processing memory of computers.

Famous producers

Well known manufacturers include Western Digital, CalDigit, Seagate, LaCie, ADATA and Samsung among others. At this amount of space the price is a little towards the steeper end.