Single-instance systems vs. multi-instance systems

Content Intelligence Installation Guide

Part Number

A system can have a single instance or can have multiple instances (four or more).

  • Every instance must meet the minimum RAM, CPU, and disk space requirements.
  • Three instances are sufficient to perform leader election for distributing work. However, a multi-instance system needs a minimum of four instances because, with the minimum hardware requirements, three instances are not sufficient for running all HCI services at their recommended distributions.
  • Hitachi Vantara has qualified HCI systems with up to 16 instances.

One instance

A single-instance system is useful for testing and demonstration purposes. It needs only a single server or virtual machine and can perform all product functionality.

However, a single-instance system has these drawbacks:

  • Only a single point of failure. If the instance hardware fails, you lose access to the system.

  • With no additional instances, you cannot choose where to run services. All services run on the single instance.

Multiple instances

A multi-instance system is suitable for use in a production environment because it offers these advantages over a single-instance system:

  • You can control how services are distributed across the multiple instances, providing improved service redundancy, scale out, and availability.
  • A multi-instance system can survive instance outages. For example, with a four-instance system running the default distribution of services, the system can lose one instance and still remain available.
    Note: For a search index to survive an instance outage:
    • The system must have at least two instances running the Index service.
    • The Index Protection Level for the index must be at least 2.

    For more information, see the HCI Administrator Help, which is available in the Admin App.

  • Performance is improved as work can be performed in parallel across instances.

  • You can add additional instances to the system at any time.

Note: You cannot change a single-instance system into a production-ready multi-instance system by adding new instances. This is because you cannot add master instances. Master instances are special instances that run a particular set of Content Intelligence services. Single-instance systems have one master instance. Multi-instance systems have at least three.

By adding additional instances to a single-instance system, your system still has only one master instance, meaning there is still a single point of failure for the essential services that only a master instance can run.

For information about adding instances to an existing HCI system, see the Content Intelligence Administrator Help, which is available from the Admin App.

Two-instance system considerations

Two-instance systems are a viable option for the HCM use case, but not recommended for Hitachi Content Search.

Three-instance system considerations

Three-instance systems should have only a single master instance. If you deploy a three-instance system where all three instances are masters, the system might not have enough resources to do much beyond running the master services.