Merge branch 'elasticsearch-sizing-requirements-docs' into 'master'

Document elasticsearch sizing requirements

Closes gitlab-elasticsearch-indexer#17

See merge request gitlab-org/gitlab-ee!6113

doc/integration/elasticsearch.md

@@ -9,10 +9,10 @@ This document describes how to set up Elasticsearch with GitLab. Once enabled,
 you'll have the benefit of fast search response times and the advantage of two
 special searches:
 
-- [Advance Global Search](../user/search/advanced_global_search.md)
+- [Advanced Global Search](../user/search/advanced_global_search.md)
 - [Advanced Syntax Search](../user/search/advanced_search_syntax.md)
 
-## Requirements
+## Version Requirements
 
 | GitLab version | Elasticsearch version |
 | -------------- | --------------------- |
@@ -37,6 +37,18 @@ service.
 You can follow the steps as described in the [official web site][install] or
 use the packages that are available for your OS.
 
+## System Requirements
+
+Elasticsearch requires additional resources in excess of those documented in the
+[GitLab system requirements](../install/requirements.md). These will vary by
+installation size, but you should ensure **at least** an additional 8 GiB of RAM
+for each Elasticsearch node, per the [official guidelines](https://www.elastic.co/guide/en/elasticsearch/guide/current/hardware.html).
+
+Storage requirements also vary based on installation side, but as a rule of
+thumb, you should allocate the total size of your production database, **plus**
+two-thirds of the total size of your git repositories. Efforts to reduce this
+total are being tracked in this epic: [gitlab-org&153](https://gitlab.com/groups/gitlab-org/-/epics/153).
+
 ## Enabling Elasticsearch
 
 In order to enable Elasticsearch, you need to have admin access. Go to