Merge pull request #3448 from ahardin-rh/etcd-hardware-recommendations

Bug 1281651, added sizing guidelines for etcd service nodes

Author: ahardin-rh

install_config/install/prerequisites.adoc

@@ -70,7 +70,7 @@ ifdef::openshift-enterprise[]
 * Base OS: RHEL 7.3 or later with "Minimal" installation option, or RHEL Atomic
 Host 7.3.2 or later. RHEL 7.2 is also supported using Docker 1.12 and its dependencies.
 endif::[]
-* NetworkManager 1.0 or later
+* NetworkManager 1.0 or later.
 * 1 vCPU.
 * Minimum 8 GB RAM.
 * Minimum 15 GB hard disk space for the file system containing *_/var/_*.
@@ -79,7 +79,13 @@ back end; see xref:configuring-docker-storage[Configuring Docker Storage]
 below.
 
 |External etcd Nodes
-|Minimum 20 GB hard disk space for etcd data.
+a|* Minimum 20 GB hard disk space for etcd data.
+* Consult
+link:https://github.com/coreos/etcd/blob/master/Documentation/op-guide/hardware.md#hardware-recommendations[Hardware
+Recommendations] to properly size your etcd nodes.
+* Currently, {product-title} stores image metadata in etcd. You must periodically
+prune old images. If you are planning to leverage a large number of images,
+place etcd on machines with large amounts of memory and fast SSD drives.
 |===
 
 [IMPORTANT]