RAID

Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks (RAID) is a technology that is used to combine disks and provide redundancy, better performance or both! Why are we talking about disks in a virtualization class you might wonder. When setting up a server it will most likely have a RAID controller in it. You will probably have to configure the RAID controller prior to installing your type-1 hypervisor. There are various types of RAID, so we need to understand the most common ones.

RAID Level 0

RAID 0 provides better performance, but does not provide any redundancy. If both disks are 1 TB the type-1 hypervisor would see this as a 2 TB drive. You would gain some performance increase as you do write to multiple drives at the same time. If one drives fails you would lose all your data.

RAID Level 1

RAID 1 provides you with complete redundancy of data. Disk 0 and Disk 1 are an exact copy. If one of the disks goes bad your data is still safe as you have a complete backup with the other disk.

RAID 5

This is the RAID level I use the most. RAID 5 provides a performance increase due to writing to several disks at once and also provides redundancy due to having a parity bit. In the image to the right you can see the files are broken up and written across multiple drives. The parity bit is noted with the p. The parity bit provides a means of redundancy as if one disk fails you can perform an Exclusive OR calculation to determine what value is missing (0 or 1) and fix it.

RAID Levels

Keep mind that the these are only 3 levels of RAID. More do exist and you can even combine them! If you want to learn about some combined RAID levels, go and read about RAID 10 and RAID 50.

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