Merge pull request #188362 from zxue/master

Update autoscale doc for Azure API for FHIR

Author: v-shils

articles/healthcare-apis/azure-api-for-fhir/autoscale-azure-api-fhir.md

@@ -5,7 +5,7 @@ author: stevewohl
 ms.service: healthcare-apis
 ms.subservice: fhir
 ms.topic: conceptual
-ms.date: 07/26/2021
+ms.date: 02/11/2022
 ms.author: zxue
 ---
 
@@ -17,7 +17,11 @@ The Azure API for FHIR as a managed service allows customers to persist with FHI
 
 By default, the Azure API for FHIR is set to manual scale. This option works well when the transaction workloads are known and consistent. Customers can adjust the throughput `RU/s` through the portal up to 10,000 and submit a request to increase the limit. 
 
-With autoscale, customers can run various workloads and the throughput `RU/s` are scaled up and down automatically without manual adjustments.
+The autoscale feature is designed to scale computing resources including the database throughput `RU/s` up and down automatically according to the workloads, thus eliminating the manual steps of adjusting allocated computing resources. 
+
+## What is the guidance on when to enable autoscale?
+
+In general, customers should consider autoscale when their workloads vary signficantly and are unpredictable. 
 
 ## How to enable autoscale?
 
@@ -26,9 +30,15 @@ To enable the autoscale feature, you can create a one-time support ticket to req
 > [!NOTE]
 > The autoscale feature isn't available from the Azure portal.
 
+## How to migrate to manual scale?
+
+A support ticket is required to change autoscale to manual scale and specify the throughput RU/s. The minimum value for manual scale you can set it to is: `MAX (400, highest max RU/s ever provisioned / 100, current storage in GB * 40)`, rounded to the nearest 1000 `RU/s`. The numbers used here are different from those used in autoscale.
+
+Once the change is completed, the new billing rates will be based on manual scale.
+
 ## How to adjust the maximum throughput RU/s?
 
-When autoscale is enabled, the system calculates and sets the initial `Tmax` value. The scalability is governed by the maximum throughput `RU/s` value, or `Tmax`, and scales between `0.1 *Tmax` (or 10% `Tmax`) and `Tmax RU/s`. 
+When autoscale is enabled, the system calculates and sets the initial `Tmax` value. The scalability is governed by the maximum throughput `RU/s` value, or `Tmax`, and scales between `0.1 *Tmax` (or 10% `Tmax`) and `Tmax RU/s`. The `Tmax` increases automatically as the total data size grows. To ensure maximum scalability, the `Tmax` value should be kept as-is. However, customers can request that the value be changed to something betweeen 10% and 100% of the `Tmax` value.
 
 You can increase the max `RU/s` or `Tmax` value and go as high as the service supports. When the service is busy, the throughput `RU/s` are scaled up to the `Tmax` value. When the service is idle, the throughput `RU/s` are scaled down to 10% `Tmax` value.
 
@@ -43,16 +53,26 @@ You can adjust the max `RU/s` or `Tmax` value through the portal if it's a valid
 >[!Note] 
 >As data storage grows, the system will automatically increase the max throughput to the next highest RU/s that can support that level of storage.
 
+## How to estimate throughput RU/s required?
 
-## How to migrate to manual scale?
+The data size is one of several factors used in calculating the total throughput RU/s required for manual scale and autoscale. You can find the data size using the Metrics menu option under **Monitoring**. Start a new chart and select "Cosmos DB Collection Size" in the Metric dropdown box and "Max" in the "Aggregation" box. 
 
-A support ticket is required to change autoscale to manual scale and specify the throughput RU/s. The minimum value for manual scale you can set it to is: `MAX (400, highest max RU/s ever provisioned / 100, current storage in GB * 40)`, rounded to the nearest 1000 `RU/s`. The numbers used here are different from those used in autoscale.
+[ ![Screenshot of metrics_new_chart](media/cosmosdb/metrics-new-chart.png) ](media/cosmosdb/metrics-new-chart.png#lightbox)
 
-Once the change is completed, the new billing rates will be based on manual scale.
+You should be able to see the Max data collection size over the time period selected. Change the "Time Range" if necessary, for example from "Last 30 minutes" to "Last 48 Hours".
+
+[ ![Screenshot of cosmosdb_collection_size](media/cosmosdb/cosmosdb-collection-size.png) ](media/cosmosdb/cosmosdb-collection-size.png#lightbox)
+
+Use the formular to calculate required RU/s.
+
+- Manual scale: storage in GB * 40
+- Autoscale: storage in GB * 400
+
+Keep in mind that this is only an estimate based on data size and that there are other factors that affect the required RU/s.
 
 ## What is the cost impact of autoscale?
 
-The autoscale feature incurs costs because of managing the provisioned throughput units automatically. This cost increase doesn't apply to storage and runtime costs. For information about pricing, see [Azure API for FHIR pricing](https://azure.microsoft.com/pricing/details/azure-api-for-fhir/).
+The autoscale feature incurs costs because of managing the provisioned throughput units automatically. The actual costs depend on hourly usage, but keep in mind that there are minimum costs of 10% of `Tmax` for reserved throughput RU/s. However, this cost increase doesn't apply to storage and runtime costs. For information about pricing, see [Azure API for FHIR pricing](https://azure.microsoft.com/pricing/details/azure-api-for-fhir/).
 
 >[!div class="nextstepaction"]
 >[About Azure API for FHIR](overview.md)