The primary difference between a “personal cloud”, NAS, and RAID is where your files are stored. With personal cloud data storage, your files are on a server connected to the internet that is owned by a third party. However, NAS configurations are typically housed in your home or business and you own the hardware that stores your files. RAID is a little different from personal cloud data storage and NAS because it deals with the way the hard drives storing your files are setup.
To some, the concept of a personal cloud is still being decided, others have chosen to focus on only the data storage aspect of a personal cloud. This concept means different things to different people, so we'll focus on the data storage bit here.
Storing your data using personal cloud data services can make your files available to you over the internet. This means you can access, edit, and save your files using your home computer, or the computer at the library. The files are stored on a server that is owned by a third party and you rent that storage space. Most services offer a free introductory service level that will get you started with personal cloud storage. However, their goal is to encourage you to upgrade to a higher service level. This company takes care of any hardware failures and creates backup copies of your data. All you have to do is upload your files and keep paying your bill.
Network Attached Storage (NAS)
It's easy to buy an external hard drive and connect it to one of your computers for additional data storage and backups. However, many homes and businesses have multiple computers and don't want to buy an external hard drive for each one. It would be much better if the external hard drive could be connected directly to the wired or wireless network that is already shared by all the computers, and this is exactly what a NAS device does. Once a NAS device is connected to your network you can share access to that device with all the computers on the network. Many NAS devices also come with software that will allow you to share access to the device over the internet. This way you can access your files even when you're away from home or the office.
Redundant Array of Independent/Inexpensive Disks (RAID)
A RAID system is one of several possible configurations that is designed to bring together multiple hard drives for expanded storage, redundancy, or both. A RAID system is used in all cloud data storage configurations and some NAS devices as well. RAID systems allow a computer to utilize multiple hard drives as a single disk. They can also be configured to write data to multiple disks in such a way that no data will be lost if one drive fails.