Many mechanical and electrical systems use redundancy to operate and supply devices that act as an insurance factor in order to allow the device to operate in case of failure. Redundancy can occur in two forms 1+1, and Net +1. Both are important, but they are operate differently because they support the primary system in different ways.
1+1 redundancy is an important component dealing with the devices that keep an operation working. For instance, on a jet plane there will be multiple jet engines. Should one fail to operate, the other or others can continue to operate and keep the plane in the air.
Another example occurs at the biological level with the dual kidney system. Here is a biological body part that cleans the blood; which without it the body would die from its own bacterial pollution. Unfortunately for the human body, there are very few 1 + 1 redundant systems. There are the eyes and ears and to a certain extent the arms and legs; but nothing else.
In the case of 1 + 1 redundancy, the identical systems work simultaneously and in conjunction to keep the overall system in operation. Computers can have dual power supplies. If one goes down, the other keeps the computer operating. With 1 + 1 redundancy, failure is an option, because the main system will continue to operate.
Net + 1 Redundancy
Net + 1 redundancy is similar but it acts as a backup and not as a functional and identical part of the system. For example, a hand brake on an automobile is a backup to the main breaking system on a vehicle. At other times Net + 1 redundancy can occur by providing an alternative operation to the main system. Using the vehicle breaking example one can also break by changing gears on the transmission. It might break and ruin the transmission but it is certainly a breaking option.
There are options for NET + 1 redundancy that normally do not appear at first glance. There is the possibility of ad-hoc innovation to make a system work. A movie appeared earlier in 2011 called Unstoppable. It was about a runaway train. When it was discovered that there was no one on the engine to stop the train and that the braking system was not engaged a second set of engineers went after the train to stop it. They did two things, the hooked up to the back of the train and used their own breaking system to slow down the train. The engineer also went car by car to engage the manual brakes to stop the runaway train.
These two examples show that with Net + 1 redundancy innovation is possible. Here failure is not an option because the main system does not have a replacement to work with.
One of the more important developments in the computer and networking industry is the use of redundancy. Computers and networks are data driven and must operate on a 24/7 basis. A computer uses the 1 + 1 redundancy with its power supplies, where dual power systems run simultaneously to keep a computer system operational. When a UPS system is also provided, which engages when the main power supply stops working, that would make it a Net + 1 system.
Costs are important factors in deciding whether to use a 1+1 system or a Net + 1 system. An exact duplicate of the system in question may be expensive. However, alternatives may do the job just as well. In computer systems, one way to have redundancy in the data is with a mirrored drive or raid system. With a mirror system an exact duplicate of the hard drive is online, so if the original hard drive goes down, then the mirror is put on line automatically. This is a 1 + 1 system.
A better system is RAID. That stands for Redundant Array of Independent Disks. In this system there are at least three hard drives. If one drive goes bad, the other two rebuild the data on the third drive while it is on and the computer operation continues to function. This is a Net + 1 redundant system because it supports the primary function of a hard drive, but it is not identical. The costs of this system are higher than a single duplicate system, but the continued operation of the computer offsets that.
The Cloud is the Internet, but it is different. The Cloud has a termination point; that is a datacenter. In contrast to the Internet, where there is no specified end-point, the Cloud services operate by storing data for a business, or performing server operations on line instead of at the local business. This system is a Net + 1 redundant system because the main computer operations can be performed off line, but for cost and efficiency the on-line element is better.
Both 1+1 and Net +1 redundancy systems are important, but the Net + 1 allows for more innovation. The Computer systems show it, and the Cloud uses it. You can see it in many day-to-day activities.
Hot-Standby 1+1 Redundancy, Cisco Systems
Authorize.net Outage Forces Online Stores To Think About Redundancy, eCommerce Wire
Ken Johnston, 1+1 Redundancy Just Isn’t Good Enough, MSDN Blogs