A stretched cluster, sometimes called as a metro cluster or metro storage cluster, is a deployment model in which two or more host servers are part of the same logical cluster but are located in separate geographical locations, usually two sites. In a stretched cluster, the two groups of servers (in each site) are usually used to provide HA and load balancing features and capabilities.

This allows the proactive behavior to avoid or minimize service outages, using disaster avoidance; if a disaster affects an entire site, the second one will manage all the resources and services. Although a stretched cluster can be used for disaster recovery and not only for disaster avoidance, there are some possible limitations on using a stretched cluster as DR as well:

• A stretched cluster can't protect you from site link failures and can be affected by the split brain scenario.
• A stretched cluster usually works with synchronous replication; that means limited distance, but also makes it difficult to provide multiple restore points with different timings.
• Bandwidth requirements are really high, to minimize storage latency. So you need not just reliable lines but also larger ones.
• A stretched cluster can be more costly than a DR solution, but of course, can also provide disaster avoidance for some cases.

In most cases where a stretched cluster is used, there could be a third site acting as a traditional DR; in this way, a multi-level protection approach is used.