RAID stands for Redundant Array of Independent Disks
We have 4 RAID levels
RAID 0
RAID 1
RAID 5
RAID 10
RAID 0 is not even useful as we do not maintain a copy of data, we simply save 50% data in one disk and the other 50% in another disk.
RAID 1, we maintain a copy of data in another disk and it is useful in case of single point failure.
RAID 5 requires mininimum 3 disks, what happens in RAID 5 is we store data along with a parity and when there is a disk failure we use this to reconstruct the data. The only didsadvantage here is parity will take up large space.
RAID 10 is combination of RAID0 and RAID1. We need minimum of 4 disks for RAID10.It takes advantages from both RAID0 speed and RAID1 fault tolerance but the disadvantage is we can only use 50% of data.