# Initial index allocation

**URL:** <https://discuss.elastic.co/t/initial-index-allocation/18861>\
**Category:** Elasticsearch\
**Created:** [July 24, 2014, 12:47pm UTC](https://discuss.elastic.co/t/initial-index-allocation/18861 "2014-07-24T12:47:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![natelapp](https://avatars.discourse-cdn.com/v4/letter/n/bcef8e/32.png) [@natelapp](https://discuss.elastic.co/u/natelapp)\
**Post date:** [July 24, 2014, 12:47pm UTC](https://discuss.elastic.co/t/initial-index-allocation/18861/1 "2014-07-24T12:47:07Z")

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We're about to stand up an elasticsearch cluster and we're facing the task  
of determining the correct number of shards to allocate for our single  
index. We have 30 servers (16cpus, 48gb memory), each of which hosting one  
node. The concern is only with query performance. Indexing performance is  
not important.

In our research on elasticsearch, it seems that one of the biggest for  
query performance is being able to fit the entire index in memory.  
However, we've also seen where having less shards / more replicas will also  
increase query performance.

I see two paths, both assuming a single shard per node:

OPTION 1: allocate 30 primary shards - the shards of the index will be  
small enough to fit in OS cache on each node, but every query will have to  
hit 30 shards. ( there's no great way to utilize "routing" here. Assume  
each query will hit all shards.)

OR

OPTION 2: allocate 10 primary shards, with 2 replicas - the shards of the  
index will NOT be small enough to fit in OS cache on each node, but a query  
will only have to hit 10 of the shards, distributed among the 30 nodes.

So, generally speaking, which is more important to query performance?  
Being able to fit the entire index in OS cache? Or less shards / more  
replicas?

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 6, 2017, 1:13am UTC](https://discuss.elastic.co/t/initial-index-allocation/18861/2 "2017-07-06T01:13:30Z")

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