When shopping to expand the storage for your Mac, the common solution is to purchase an external storage where you connect via the USB or Firewire port of your Mac. The other option is NAS (Network Attached Storage), which is a storage device that you access via the network.
A NAS is actually a self-contained small computer build for storage purpose. There are many vendors offering NAS products such as Synology, Qnap and Netgear. Even Western Digital and Seagate now offers NAS storage. One of the advantage touted by NAS vendors is the RAID feature found on most NAS.
With proper RAID setup in NAS, you can prevent loss of data in the event of a harddisk failure. For example, if you have 3 units of 3TB harddisk setup in a RAID 5 configuration, you’ll get 6TB (3TBx2) of usable space, with the extra 2TB used for redundancy. With this setup, you are protected with one harddisk failure at a time. When one of the harddisk fails, your data is still there, and you can plug in a replacement to restore back to normal working condition. But when two harddisks fail at the same time, you data is gone.
One area that is often neglected by marketing literature of NAS product is that RAID does not protect against the failure of the NAS device itself. When your NAS device failed (not the hard disks), you have to pray that it can be repaired. There is no guarantee that moving your hard disks to a new NAS will work. There could be differences in firmware version or you can not find the same model replacement for your failed NAS. The risk of complete data loss is there.
Modern NAS has GUI interface that makes their management as easy as possible. NAS is an attractive option especially for sharing media among family members. It does however pays to understand the RAID feature in your NAS and the protection level of your setup. And NAS needs backup.