In this course, you'll get a clear idea of what each one is, and how they differ. This is a question that gets asked a lot, I hear it from people who have had years of experience within the IT industry, and those who are new and just starting out.
Either way, there is clearly some confusion between the two, and understandably so. They both ultimately have the same goal, to keep your systems up and running should something fail within your architecture, but there is a difference. High Availability can be defined by maintaining a percentage of uptime which maintains operational performance, and so this can closely be aligned to an SLA.
In fact, AWS has many SLAs for its services where they implement their own level of resilience and management to maintain that level of high availability. Within a region we could use two different availability zones, and in each AZ we could have two EC2 instances, which are all associated with an Elastic load balancer.
So in this example we have different elements contributing to a highly available solution. We have the use of two AZs and additional EC2 instances. So if an instance fails, we still have plenty of compute resources, or if an entire AZ fails then we still have the minimum of two instances to maintain the required SLA. High availability systems are an excellent solution for applications that must be restored quickly and can withstand a short interruption should a failure occur.
Some industries have applications so time-critical that they cannot withstand even a few seconds of downtime. Many other industries, however, can withstand small periods of time when their database is unavailable. Fault-tolerant systems instantly transition to a new host, whereas high-availability systems will see the VMs fail with the host before restarting on another host. VMware High Availability should be used to maintain uptime on important but non-mission-critical VMs.
While HA cannot prevent VM failure, it will get VMs back up and running with very little disturbance to the virtual infrastructure. Consider the value of HA for host failures that occur in the early hours of the morning, when IT is not immediately available to resolve the problem. VMware vSphere Fault Tolerance has been around since If your company cannot withstand downtime for end users, VMware FT or a similar tool is required. You are commenting using your WordPress.
You are commenting using your Google account. You are commenting using your Twitter account. Fault tolerant solutions traditionally consist of a pair of tightly coupled systems which provide redundancy. Generally speaking this involves running a single copy of the operating system and the application within, running consistently on two physical servers.
The two systems are in lock step, so when any instruction is executed on one system, it is also executed on the secondary system. A good way to think of it is that you have two separate machines that are mirrored. In the event that the main system has a hardware failure, the secondary system takes over and there is zero downtime. So which solution is right for you? Well, the initial and obvious conclusion most instantly come to is that 'no' downtime is better than 'some' downtime, so FT must be preferred over HA!
Zero downtime is also the ultimate IT utopia which we all strive to achieve, which is goodness. Also FT is pretty cool from a technology perspective, so that tends to get the geek in all of us excited and interested. However, it is important to understand they protect against different types of scenarios It is true that FT solutions provide great resilience to hardware faults, such as if you walk up and yank the power cord out of the back of the server However, remember that FT solutions are running a common operating system across those systems.
In the event that there is a software fault such as a hang or crash , both machines are affected and the entire solution goes down. There is no protection from software fault scenarios and at the same time you are doubling your hardware and maintenance costs.
0コメント