Planning to buy an external HDD for backup?

I just ran into my friends on the parking lot while taking out my plastic bottles to the recycles, and at the conversation ended with something about backing up data in the external HDD.


This is a crude and subjective external HDD buying guide.


1. Capacity
Of course it should be large enough to hold your data, but you may want to consider making multiple backups. The system administrator in my lab backs up everything once a week, and he keeps this back-ups for a couple of months. You don't have to back things up once a week, but having a multiple copy can be useful.
I have 500GB FreeAgent from Seagate. I have about 120GB of important stuff, and I keep at least 2 copies of them. See the pictures below.

My 2 recent back-ups

I saved my data at the end of last year, and again about 3 weeks later. The reason for multiple copies is because you may make changes and overwrite your old back-ups, then say, "wait I need that file again".
Multiple copies prevent that from happening.
So, the good size is 4x(your data size). With this size you can have extra space for something else.



2. 2.5" or 3.5"
This is the size (diameter) of the disc in the drive. 2.5" is smaller and lighter, yet slow. 3.5" is faster but usually requires external power source. Because it needs external power, it's a bit hassle to carry around. If you're planning to travel a lot with it, get 2.5".



3. Connectivity
In the past USB 2.0 was very popular choice, but now it's giving a way to USB 3.0 and e-SATA. Get USB3.0 and/or e-SATA. Of course your computer should have USB 3.0 or e-SATA port. If you don't have USB 3.0 post yet, but planning to get a new computer soon, get USB 3.0 anyway. It'll work just fine with USB 2.0 port. At some point IEEE1394 (aka FireWire) drew quite a bit of attention, but Microsoft decided not to support that any longer on Windows 8 since USB 3.0 already exceeds the speed of FireWire.

Speed comparison. Do you see USB 3.0 there?