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ClustrixDB Xpand allows clusters to be deployed across multiple zones to provide fault tolerance during unplanned zone failure. A zone in ClustrixDB Xpand is grouping of nodes, such as AWS Availability Zones within the same Region, different server racks, different network switches, different power sources, or even separate servers in different data centers. ClustrixDB Xpand requires that network latency between zones not exceed 2ms.  

Table of Contents

When ClustrixDB Xpand is configured for zones, the Rebalancer becomes zone-aware and ensures replicas are placed in different zones. Additionally, Paxos accepters are distributed across multiple zones. The result is that ClustrixDB Xpand is fault tolerant in the face of unexpected zone failure, regardless of how many nodes are in the zone. 

Prerequisites

Use of zones with ClustrixDB Xpand has the following prerequisites: 

  • Clustrix Xpand supports configurations with a minimum of 3 and a maximum of 5 zones. 
  • There must be a sufficient number of zones to maintain a quorum of nodes following a failure 
  • Zones must be in the same geographical region with <2ms network latency between each zone.
  • A cluster deployed across zones must have the same number of nodes in each zone. 

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There must be the same number of nodes in each zone. Clustrix  Xpand recommends deploying a 9 node cluster across 3 zones.

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To configure zones, use ALTER CLUSTER ZONE to assign nodes to a zone. Zone ids must be greater than 0 and there must be an equal number of nodes in each zone. For example, a 9 node cluster deployed across 3 zones should have 3 nodes each in zones 1, 2, and 3.

Clustrix Xpand recommends provisioning enough free disk space to reprotect the data after a zone failure. See Allocating Disk Space for Fault Tolerance and Availability .

Note

Clustrix Xpand currently supports a minimum of 3 and a maximum of 5 zones. 

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  1. Temporarily disable the Rebalancer.
  2. Provision nodes in new zones and install ClustrixDB Xpand on each node. 
  3. Use the Flex Up procedure to add the new nodes to the cluster.
  4. Configure zones using ALTER CLUSTER ZONE.
  5. Use the Flex Down procedure to remove surplus nodes from the cluster. 
  6. Re-enable the Rebalancer. 

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For further information, see Understanding Fault Tolerance in ClustrixDBXpand.