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Chen, Junjie
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Reviewed-by: Mützel, Andrea <andrea.muetzel@t-systems.com> Co-authored-by: Chen, Junjie <chenjunjie@huawei.com> Co-committed-by: Chen, Junjie <chenjunjie@huawei.com>
29 lines
4.0 KiB
HTML
29 lines
4.0 KiB
HTML
<a name="dcs-pd-200312004"></a><a name="dcs-pd-200312004"></a>
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<h1 class="topictitle1">Basic Concepts</h1>
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<div id="body8662426"><div class="section" id="dcs-pd-200312004__en-us_topic_0145956240_section21221334179"><h4 class="sectiontitle">DCS Instance</h4><p id="dcs-pd-200312004__en-us_topic_0145956240_p101241051105714">An instance is the minimum resource unit provided by DCS.</p>
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<p id="dcs-pd-200312004__p944455984115">For details, see <a href="en-us_topic_0054235835.html">DCS Instance Specifications</a> and <a href="dcs-pd-200312001.html">DCS Instance Types</a>.</p>
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<div class="section" id="dcs-pd-200312004__en-us_topic_0145956240_section8561162475017"><h4 class="sectiontitle">Project</h4><p id="dcs-pd-200312004__en-us_topic_0145956240_p856122425013">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.</p>
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<div class="section" id="dcs-pd-200312004__en-us_topic_0145956240_section19747132512175"><h4 class="sectiontitle">Maintenance Time Window</h4><p id="dcs-pd-200312004__en-us_topic_0145956240_p12559323191911">The maintenance time window is the period when the DCS service team upgrade and maintain the instance.</p>
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<p id="dcs-pd-200312004__en-us_topic_0145956240_p161692619209">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.</p>
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<p id="dcs-pd-200312004__en-us_topic_0145956240_p619362811710">When creating an instance, you must specify a maintenance time window, which can be modified on the <strong id="dcs-pd-200312004__b139802465415">Basic Information</strong> page after the instance is created.</p>
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<p id="dcs-pd-200312004__en-us_topic_0145956240_p6683155115346">For details, see: <a href="dcs-ug-0312025.html">Modifying Maintenance Time Window</a>.</p>
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<div class="section" id="dcs-pd-200312004__en-us_topic_0145956240_section27941513183211"><h4 class="sectiontitle">Cross-AZ Deployment</h4><p id="dcs-pd-200312004__en-us_topic_0145956240_p187388152325">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.</p>
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<p id="dcs-pd-200312004__p18724141752918">When creating a master/standby or cluster DCS Redis instance, you can select a standby AZ for the node.</p>
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<div class="section" id="dcs-pd-200312004__en-us_topic_0145956240_section20999323134412"><a name="dcs-pd-200312004__en-us_topic_0145956240_section20999323134412"></a><a name="en-us_topic_0145956240_section20999323134412"></a><h4 class="sectiontitle">Shard</h4><p id="dcs-pd-200312004__en-us_topic_0145956240_p485319256447">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.</p>
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<p id="dcs-pd-200312004__p1728812129347">Each cluster instance consists of multiple shards. By default, each shard is a master/standby instance with two replicas. The number of shards is equal to the number of master nodes in a cluster instance.</p>
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<div class="section" id="dcs-pd-200312004__section935811803314"><h4 class="sectiontitle">Replica</h4><p id="dcs-pd-200312004__p4358131883312">A replica is a node in a DCS instance. A single-replica instance has no standby node. A two-replica instance has one master node and one standby node. By default, each master/standby instance has two replicas. If the number of replicas is set to three for a master/standby instance, the instance has one master node and two standby nodes. A single-node instance has only one node.</p>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="dcs-pd-0326001.html">Service Overview</a></div>
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