I want to take a closer look at one of the new features in SQL Server Denali. While everyone has been drooling over HADRON, another HA feature has gone mostly unnoticed. I haven't heard anyone talking about it yet, so this should be an introduction to this new feature, Multi-Subnet Failover Clusters.
Multi-subnet failover clusters is an enhancement to an existing technology, geographically dispersed failover clusters. SQL Server 2008 and Windows Server 2008 introduced geographically dispersed failover clusters, often called stretch clusters or geo-clusters. It allows you to stretch a cluster across mutliple data centers to provide a greater level of availability and also provides protection at the storage level by having more than a single copy of the data.
The downside of a geo-cluster that you cannot simply select two datacenters and set up a geo-cluster. Implementing a geo-cluster requires a stretch VLAN so that all nodes are in the same subnet. Currently, SQL Server failover clustering does not support multiple subnets. A geocluster allows quick failover between all nodes of the cluster; however, failover between nodes in the same site is measurably faster.
This post was cross-posted from the main SQLSoldier blog. Please visit the source blog to read the whole post and leave a comment: http://www.sqlsoldier.com/wp/sqlserver/multsubnetfailoverclusters