RAID LEVEL 5

     RAID 5 is by far the most common RAID configuration for business servers and enterprise NAS devices.
This RAID level provides better performance than mirroring as well as fault-tolerance. With RAID 5, data and parity (which is additional data used for recovery) are striped across three or more disks. Disk drives typically fail in sectors, rather than the entire drive dying.
When RAID 5 is configured, if a portion of a disk fails, that data gets recreated from the remaining data and parity, seamlessly and automatically.
This is beneficial because RAID 5 allows many NAS and server drives to be "hot-swappable" meaning in case a drive in the array fails, that drive can be swapped with a new drive without shutting down the server or NAS and without having to interrupt users who may be accessing the server or NAS.
RAID 5 can be implemented as a software or hardware solution.
The downside to RAID 5 is the performance hit to servers that perform a lot of write operations.

Graphical representation of the RAID layout:

Raid Level 5