diff --git a/CLUSTER_MGMT.md b/CLUSTER_MGMT.md index 531e4442..9dd95559 100644 --- a/CLUSTER_MGMT.md +++ b/CLUSTER_MGMT.md @@ -5,9 +5,9 @@ This document describes, in detail, how to create and manage a rqlite cluster. Clusters of 3, 5, 7, or 9, nodes are most practical. Clusters with a greater number become unweildy. ## Clusters with an even-number of nodes -There is no point running clusters with even numbers of nodes. To see why this imagine you have one cluster of 3 nodes, and a second of 4 nodes. In both cases a majority of nodes are required for the cluster to reach consensus. A majority is defined as `N/2 + 1` where `N` is the number of nodes in the cluster. For a 3-node a majority is 2; for a 4-node cluster a majority is 3. Therefore a 3-node cluster can tolerate the failure of a single node, and 4-node cluster can also only tolerate a failure of a single node. A 4-node cluster is no more fault-tolerant than a 3-node cluster, so running a 4-node cluster provides no advantage over a 3-node cluster. Only a 5-node cluster can tolerate the failure of 2 nodes. +There is no point running clusters with even numbers of nodes. To see why this is imagine you have one cluster of 3 nodes, and a second of 4 nodes. In both cases a majority of nodes are required for the cluster to reach consensus. A majority is defined as `N/2 + 1` where `N` is the number of nodes in the cluster. For a 3-node a majority is 2; for a 4-node cluster a majority is 3. Therefore a 3-node cluster can tolerate the failure of a single node, and 4-node cluster can also only tolerate a failure of a single node. -An analogous argument applies to 5-node vs. 6-node clusters, and so on. +So a 4-node cluster is no more fault-tolerant than a 3-node cluster, so running a 4-node cluster provides no advantage over a 3-node cluster. Only a 5-node cluster can tolerate the failure of 2 nodes. An analogous argument applies to 5-node vs. 6-node clusters, and so on. # Creating a cluster