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Initial v Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com> Co-authored-by: proposalbot <proposalbot@otc-service.com> Co-committed-by: proposalbot <proposalbot@otc-service.com>
51 lines
2.3 KiB
ReStructuredText
51 lines
2.3 KiB
ReStructuredText
:original_name: dcs-pd-200312004.html
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.. _dcs-pd-200312004:
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Basic Concepts
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==============
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DCS Instance
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------------
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An instance is the minimum resource unit provided by DCS.
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DCS supports the Redis cache engine, and single-node, master/standby, and cluster instance types. For each instance type, multiple specifications are available.
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For details, see :ref:`DCS Instance Specifications <en-us_topic_0054235835>` and :ref:`DCS Instance Types <dcs-pd-200312001>`.
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Project
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-------
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Projects are used to group and isolate OpenStack resources (computing resources, storage resources, and network resources). A project can be a department or a project team. Multiple projects can be created for one account.
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Replica
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-------
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A replica is a node of a DCS instance. No replication indicates that the instance does not have a standby node. Master/Standby replication indicates that the instance has a standby node. For example, a master/standby DCS instance has a master/standby replication. Each node of a cluster DCS Redis instance has a master/standby replication.
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Maintenance Time Window
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-----------------------
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The maintenance time window is the period when the DCS service team upgrade and maintain the instance.
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DCS instance maintenance takes place only once a quarter and does not interrupt services. Even so, you are advised to select a time period when the service demand is low.
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When creating an instance, you must specify a maintenance time window, which can be modified on the **Basic Information** page after the instance is created.
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For details, see: :ref:`Modifying Maintenance Time Window <dcs-ug-0312025>`.
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Cross-AZ Deployment
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-------------------
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Master/Standby instances are deployed across different AZs with physically isolated power supplies and networks. Applications can also be deployed across AZs to achieve HA for both data and applications.
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When creating a master/standby or cluster DCS Redis instance, you can select a standby AZ for the standby node.
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.. _dcs-pd-200312004__en-us_topic_0145956240_section20999323134412:
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Shard
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-----
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A shard is a management unit of a cluster DCS Redis instance. Each shard corresponds to a redis-server process. A cluster consists of multiple shards. Each shard has multiple slots. Data is distributedly stored in the slots. The use of shards increases cache capacity and concurrent connections.
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