Cross-cabling As An Interconnect (RAC)

In RAC (Real Application Cluster) interconnect is the internal channel that union all nodes in the cluster. This network within the cluster must be specialized. This focuses on the management of the same and it is based for cache fusion. The idea was not new although Oracle recreated it since version 8, if memory serves me, Oracle had create before RAC what was called Oracle Parallel Server (versions 7 and earlier). On OpenVMS VAX and using the interconnect was delegated to hardware, I used to use a Digital product (actully HP) known as “Memory Channel”, which is actually what is now called a RDMA (Read Direct Memory Access), fused memories of the nodes the cluster.

 

The theme of today’s post is to indicate that many people, as a cheap solution, use a simple cable to implement the interconnect, this basically goes for a cluster of two nodes. However, this solution have a lot of problems, please noted;

 

  • Not supported by Oracle. If there is a problem with it can become a serious problem.
  • The cross-cabling is unstable.
  • Should not be installed in Production.
  • If you lost a node, the other will take longer to detect the problem, waiting for a timeout expires.
  • Can be mounted only for two nodes, but would involve installing a soft on nodes that act as a router, but it is complex.
  • Some NIC cards do not work properly with cross-cabling.

 

Summary;

You should use a switch.

 

HTH – Antonio NAVARRO

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