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Expanding and shrinking cluster resources

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How to expand and shrink a cluster in a homogeneous Content Software for File system configuration.

NoteThe cluster expansion process described here is only applicable to a homogeneous Content Software for File system configuration, which is highly recommended. For non-homogeneous system configurations, contact your Hitachi representative.
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Expand and shrink overview

An overview of the cluster expand and shrink process in a homogeneous Content Software for File system configuration is provided.

In the Content Software for File system, it is possible to expand and shrink a cluster as follows:

  • Add or delete backend hosts
  • Add or delete SSDs from an existing backend host
  • Change the number of cores assigned to the Content Software for File system in existing backend hosts
  • Change the amount of memory allocated to the Content Software for File system in existing backend hosts
  • Change the network resources assigned to the Content Software for File system in existing backend hosts
NoteThe expansion or shrinking of networking resources is performed infrequently.
NoteThe cluster expansion process described here is only applicable to a homogeneous Content Software for File system configuration, which is highly recommended.
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Planning an expansion or shrink
NoteThe expansion of a Content Software for File system offers the opportunity to increase performance, while the shrinking of a system may reduce performance. For more details and to receive estimates contact your Hitachi representative.
NoteIn the following descriptions, cluster expansion also relates to cluster shrinking.

Expansion procedures are similar to installation instructions and can be obtained as a Content Software for File system installation procedure, available if you contact customer support. Similar to planning a new cluster, the objectives of the expansion, in terms of space and performance, need to be translated to the actual cluster resources. This process is practically a repeat of the planning process for new clusters, with the following options and limitations provided in the next sections.

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Possible expansion options
  • Addition of new backend hosts.
  • Addition of new failure domains, as long the system was installed with failure domains.
  • Addition of new SSDs to existing backend hosts.
  • Assignment of additional cores to Content Software for File in existing backend hosts.
  • Assignment of more memory to Content Software for File in existing backend hosts.
  • Assignment of additional network resources to Content Software for File in existing backend hosts.
  • Reconfiguration of hot spares.
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Expansion limitations
  • It is not possible to change the defined Content Software for File system protection scheme.
  • It is not possible to define failure domains on a system that was installed without failure domains.
  • A Content Software for File system configured with failure domains cannot be configured to be without failure domains.
  • Only the same network technology can be implemented that is, it is not possible to mix between Ethernet and InfiniBand.
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Cluster expansion process

Once an expansion of more SSDs or backend hosts has been planned and executed, the Content Software for File system starts a redistribution process. This involves the redistribution of all the existing data to be perfectly balanced between the original hosts or SSDs and newly added resources. This process can take from minutes to hours, depending on the capacity and the networking CPU resources. However, the capacity increase is instant, and therefore it is possible to define more filesystems immediately, without waiting for the completion of the redistribution process.

NoteIf necessary, contact customer support for more details on the redistribution process and its expected duration.

Once the expansion of more cores or backend hosts has been implemented, the added CPU resources are operational in less than a minute. Write performance improves almost immediately, while read performance only improves on completion of the redistribution of the data.

NoteAs part of the requirements for a homogeneous Content Software for File system configuration, when expanding memory resources, the new hosts must have the same memory as the existing hosts.
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