External hard drives are the storage devices that are mostly used to have backup of your personal data and to transfer data form one system to another system. It is not cheaper and from around $50 the rate of external hard drives is available and as much as you add terabytes to it the amount will be increasing. For $50 you can get a hard drive with a terabyte storage, which enables you to store more than 750,000 MP3s or photos, or more than 230 movie files.
External drives are of two types. That is Desktop-class drives, that are associated with 3.5-inch mechanism inside and it requires a power adapter. These are designed in such a way that they should stay in one place on the desk.
If you are in need of a desktop-class drive and want to buy one to transfer video or lots of other files, then make sure that you are buying it with a built-in fan, so that the life of the drive can be extended by extra cooling.
2.5-inch mechanisms are associated with the Notebook-class hard drive that is powered through the connector cable. A 2.5-inch model can be slipped into a coat and some pants pockets also.
Currently Desktop-class models top out at 8 terabytes per mechanism, but two to four mechanisms will be associated by some drive manufacturers into a chassis for more storage. Up to 4TB capacity the Notebook-class drives are available but commonly 500 GB to 1TB are used.
By buying an external RAID array the speed, capacity or data protection can be increased, by complexity and expense is added by multiple drives. Once a single volume external RAID array is connected to your Mac or PC, it will act and show up as any other external drive and it can become more complex after that.
A drive should be considered with RAID levels 1, 5, 10 support, if really important data is stored that you can’t afford to lose. For capacity, speed and other factors like software vs. hardware there are other RAID levels.