add reusable file, and add it to 3 articles

Author: mchammer01

content/admin/enterprise-management/about-geo-replication.md

@@ -22,6 +22,8 @@ Geo DNS, such as [Amazon's Route 53 service](http://docs.aws.amazon.com/Route53/
 
 Writing requests to the replica requires sending the data to the primary and all replicas. This means that the performance of all writes are limited by the slowest replica, although new geo-replicas can seed the majority of their data from existing co-located geo-replicas, rather than from the primary. Geo-replication will not add capacity to a {% data variables.product.prodname_ghe_server %} instance or solve performance issues related to insufficient CPU or memory resources. If the primary appliance is offline, active replicas will be unable to serve any read or write requests. 
 
+{% data reusables.enterprise_installation.replica-limit %}
+
 ### Monitoring a geo-replication configuration
 
 {% data reusables.enterprise_installation.monitoring-replicas %}

content/admin/enterprise-management/about-high-availability-configuration.md

@@ -14,6 +14,8 @@ When you configure high availability, there is an automated setup of one-way, as
 
 {% data variables.product.prodname_ghe_server %} supports an active/passive configuration, where the replica appliance runs as a standby with database services running in replication mode but application services stopped.
 
+{% data reusables.enterprise_installation.replica-limit %}
+
 ### Targeted failure scenarios
 
 Use a high availability configuration for protection against:

content/admin/enterprise-management/creating-a-high-availability-replica.md

@@ -10,6 +10,8 @@ topics:
   - enterprise
 ---
 
+{% data reusables.enterprise_installation.replica-limit %}
+
 ### Creating a high availability replica
 
 1. Set up a new {% data variables.product.prodname_ghe_server %} appliance on your desired platform. The replica appliance should mirror the primary appliance's CPU, RAM, and storage settings. We recommend that you install the replica appliance in an independent environment. The underlying hardware, software, and network components should be isolated from those of the primary appliance. If you are a using a cloud provider, use a separate region or zone. For more information, see ["Setting up a {% data variables.product.prodname_ghe_server %} instance"](/enterprise/{{ currentVersion }}/admin/guides/installation/setting-up-a-github-enterprise-server-instance).

data/reusables/enterprise_installation/replica-limit.md

@@ -0,0 +1,8 @@
+{% if  currentVersion ver_gt "enterprise-server@2.21" %}
+{% note %}
+
+**Note:** There is a maximum of 8 High Availability replicas (both passive and active/geo replicas) allowed for {% data variables.product.product_name %}.
+
+{% endnote %}
+
+{% endif %}