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What is High Availability?
High availability (HA) refers to the continuous availability of applications and data to authorized users and includes all aspects of a hardware and software environment that could fail (disk, CPU, mainframe, physical site, regional outage, etc.).
A high availability solution will protect from both planned and unplanned downtime — the first due to circumstances outside of the solution provider’s control and the second due to server and system maintenance, upgrade, backup, etc. 90% of downtime is due to planned outages. Ensuring high availability from all types of outages, planned and unplanned, is important.
Analysis of High Availability
There is a considerable amount of work that goes into analyzing HA. The weakest link of most systems is often the data storage components. Using a RAID design (Redundant Array of Independent Discs) makes data much more redundant in a useful, logical manner.
Setting up a backup service can also help with HA. This process, known as failover, relies on a switch to a remote server in times of need.
Measurements of HA
- RTO is the maximum amount of time elapsed during a disruption before the quantity of data lost during that period exceeds a predetermined threshold.
- RPO is the maximum amount of time elapsed before a disruption blocks the normal flow of operations to a predetermined extent.