RAID is an acronym standing for
"Redundant Array of Independent (or Inexpensive) Disks".
There are various RAID types which differ in three main characteristics:
- fault tolerance
These days, the most widespread array types are RAID 0, RAID 5, and RAID 1.
Since an array is a man-made device it can fail. Most often, RAID failures happen because of:
- failure of one or several member disks,
- controller failure in a hardware RAID,
- managing software failure in case of a software RAID,
- human operator error,
- natural disasters and similar external factors (floods, fires, and so on).
Since RAID is a fault tolerant storage people use it to store valuable data sometimes even ignoring backup.
In most cases it is possible to reconstruct a failed array and then read data off it.
There are several options to recover a failed RAID.