Over recent years within Europe some customers have accepted a close geographic distance (e.g. 15 km) between data centres in return for a high bandwidth, low latency interconnect (typically ‘dark’ or dedicated fibre). This is to enable them to share normal production workload across both sites – so called "active/active" data centres – which is contrary to the traditional approach of having a highly segregated Disaster Recovery (DR) site (an "active/standby" topology).
Prior to the mid-2013 Oracle supported a single approach to High Availability (HA), which was clustering within a single site, as described by Fusion Middleware High Availability Guide, and not stretched across two sites. The Oracle supported approach to Disaster Recovery was entire site fail-over using an active-standby model, as shown below (from Fusion Middleware Disaster Recovery Guide):
A few large customers had negotiated agreements with Oracle to support architectures that were simultaneously active in 2 data centres, but these were people spending considerable sums on licences and ACS support.
Over the last 5 years the cost of site-to-site fibre has fallen considerably with “metropolitan” scale data centre links becoming common. Whilst the term Metropolitan Area Network (MAN) originally meant a connection across a city, these days it tends to also apply to low latency connections between neighbouring conurbations, typically running Ethernet over DWDM. The scale of a MAN falls in between the Local Area Network (LAN) within a single data centre and the traditional Wide Area Network (WAN) which can span hundreds of miles. Read the complete article here.
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