Adding first pass of schema overview, updating 'How a sync works' include

Author: forstisabella

src/_includes/content/how-a-sync-works.md

@@ -1,6 +1,6 @@
 When Segment loads data into your warehouse, each sync goes through the following steps:
-1. **Ping:** Segment servers try to connect to your warehouse. 
-2. **Scan:** Segment finds new events and updated objects. 
-3. **Download:** Segment pulls events and objects from AWS S3 or Dynamo into a staging area.
-4. **Process:** The raw Segment event and object archive files are pulled from the staging area and transformed into database-specific formats. The [warehouse schema](/docs/connections/storage/warehouses/schema/) is also defined in this step. 
-5. **Load:** Segment de-duplicates the transformed data and loads it into your warehouse. If you have queries set up in your warehouse, they run after the data was loaded into your warehouse. 
+1. **Ping:** Segment servers connect to your warehouse. For Redshift warehouses, Segment also runs a query to determine how many slices a cluster has at this step. <br/>Common reasons a sync would fail at this step include a blocked VPN/IP, a warehouse that isn't publicly available, and user permission/credential errors. 
+2. **Scan:** Segment finds new events in AWS S3 and updated objects in Dynamo. 
+3. **Download:** Segment pulls the events and objects into a staging area.
+4. **Process:** The raw Segment event and object archive files are transformed into database-specific formats. The [warehouse schema](/docs/connections/storage/warehouses/schema/) is also defined in this step. 
+5. **Load:** Segment de-duplicates the transformed data and loads it into your warehouse. If you have queries set up in your warehouse, they run after the data is loaded into your warehouse. <br/>***This is the only step that connects to your warehouse: all other steps are internal to Segment.*** 

src/connections/storage/warehouses/schema.md

@@ -2,6 +2,8 @@
 title: Warehouse Schemas
 ---
 
+A **schema** describes the way a warehouse is organized. Schemas include all database elements: tables, views, indexes, and synonyms, and the relationships that exist between elements. 
+
 ## Warehouse tables
 
 The table below describes the schema in Segment Warehouses: