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This article introduces the relevant knowledge of "what is the concept of ha in linux". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

In linux, HA is the abbreviation of "High Availability" for high availability cluster, which can automatically switch resources and services when a single node fails, ensuring that the service is always online, thus reducing the loss caused by computer hardware and software fallibility.

The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is ha in linux

High availability cluster, High Availability Cluster, or HACluster for short, is simply a group of computers that provide users with a set of network resources as a whole. These individual computer systems are the node of the cluster.

The emergence of high-availability clusters is to make the overall services of the cluster as available as possible, thus reducing the loss caused by computer hardware and software fallibility. If a node fails, its backup node will take over its responsibilities within a few seconds. Therefore, for users, the cluster will never be down.

The main function of highly available cluster software is to automate fault checking and business switching. A highly available cluster with only two nodes is also known as a dual hot backup, even if two servers are used to back up each other. When one server fails, another server can undertake the service task, so as to automatically ensure that the system can provide services continuously without human intervention. Dual-computer hot backup is only one kind of high-availability cluster, and the high-availability cluster system can support more than two nodes, provide more and more advanced functions than dual-computer hot backup, and can better meet the changing needs of users.

High availability cluster means that when one node or server fails, another node can automatically and immediately provide services, that is, the resources on the failed node can be transferred to another node. in this way, another node can provide services with resources. High availability cluster is used to automatically switch resources and services when a single node fails, which ensures that the service is always online. In this process, it is transparent to the client.

Metrics for highly available clusters

HA (High Available), high availability clustering is measured by the reliability (reliability) and maintainability (maintainability) of the system. In engineering, the mean time between failures (MTTF) is usually used to measure the reliability of the system, and the mean maintenance time (MTTR) is used to measure the maintainability of the system. So usability is defined as: HA=MTTF/ (MTTF+MTTR) * 100%

Specific HA metrics:

99% of the downtime is no more than 4 days a year

99.9% no more than 10 hours of downtime a year

99.99% of the downtime is no more than 1 hour a year

99.999% of the downtime is no more than 6 minutes a year

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