RAID arrays appear to the operating system as a single logical hard disk, RAID has techniques of disk mirroring or disk striping.
Disk Mirroring: It copies identical data onto more than on drive
Disk Striping: It is process of dividing a data into blocks and spreading the data blocks across multiple storage devices.
On most situations you will be using one of the following levels of RAID’s
RAID 0:

Following are the key points to remember for RAID level 0.
- Minimum 2 disks.
- Excellent performance ( as blocks are striped ).
- No redundancy ( no mirror, no parity ).
- Don’t use this for any critical system
RAID 1:

Following are the key points to remember for RAID level 1.
- Minimum 2 disks.
- Good performance ( no striping. no parity ).
- Excellent redundancy ( as blocks are mirrored ).
RAID 5:

Following are the key points to remember for RAID level 5.
- Minimum 3 disks.
- Good performance ( as blocks are striped )
- Good redundancy ( distributed parity ).
- Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.
RAID 10:

Combining RAID 1 and RAID 0, this level is often referred to as RAID 10, which offers higher performance than RAID 1, but at a much higher cost. In RAID 1+0, the data is mirrored and the mirrors are striped.
Following are the key points to remember for RAID level 10.
- Minimum 4 disks.
- This is also called as “stripe of mirrors”
- Excellent redundancy ( as blocks are mirrored )
- Excellent performance ( as blocks are striped )
- If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).