In my previous article High Availability and SLA requirements for Oracle database we discussed that the successful High Availability (HA) begins with the understanding of Service Level Agreements (SLA) required by the business along with each of these dimensions. This guides important decisions on IT technology and determines the appropriate level of investment in HA architecture. Choosing the right technical solution for database system design from scratch is difficult. You can follow some best practices in building High Available Oracle database systems based on Availability Levels that match database industry standards. In this article I’ll share some best practices and my experience in architecting database systems for first 2,5 Availability Levels describing some technical solutions based on SAN, cluster, Clusterware, Oracle ASM, Cold Failover Cluster (CFC).
I’ll start with a graph below that illustrates Availability Continuum and depicts the increases in availability that can be gained with the progression between levels of availability. It is not based on empirical data, and the percentage values used are for illustrative purposes only, but being close (based on my experience) to real figures in common IT infrastructure for Oracle database environments though.
Another way to interpret the y-axis scale is as a measure of acceptable down time – the lower end of the axis represents a reasonable amount of down time as tolerable, whereas the upper end of the axis represents even the smallest amount of down time as being intolerable.