Month: August 2017

NetApp cDOT (ONTAP 9) – RDB and Cluster Replication Ring

In my last entry I have written about quorum and epsilon. In this article, I have explained that a Ontap Cluster always have a master node – often called RDB Master.  In this entry I would like to explain what RDB is. This article is valid for both NetApp cDOT (ONTAP 8.x) as well as ONTAP 9.x


A Replicated Database (often referred as RDB) is a basis of ONTAP Cluster. This database contains cluster configuration information divided into RDB units. The RDB does not contain any user data, instead it provides a single point of management of all nodes within the cluster. Continue reading

NetApp cDOT or ONTAP 9 ?

Within ONTAP 9 the naming convention has been slightly modified for the ONTAP family products. I feel I have to explain it a little bit further, since the term I’m using often (NetApp cDOT) might soon be outdated. So here are the details:

  • NetApp cDOT  – cDOT stands for clustered Data ONTAP. It is the product name for clustered-mode ONTAP 8.x. ONTAP 8.x is available in two versions: clustered and 7-mode, therefore this division.
  • ONTAP 9  – With version 9, NetApp ONTAP is available only as clustered mode (7-mode is no longer developed), therefore the product name was actually shorten from Clustered Data ONTAP  to just ONTAP.

Articles regarding NetApp cDOT are also for ONTAP 9. If some feature is only available from specific ONTAP version, I mention that in the article.

NetApp cDOT – quorum and epsilon

In today’s entry I would like to introduce quorum and epsilon concepts. Both are related with cluster health, needed in case of potential communications and connectivity issues.

What is Quorum?

When a cluster is in quorum, it means that majority of nodes are healthy and can communicate with each other. In other words, quorum is a precondition for a functioning cluster. When quorum is lost, the cluster does not have the ability to accomplish normal operations. Continue reading