Described scaling latency with PFS storage

Author: dimitri-furman

articles/sql-database/sql-database-single-database-scale.md

@@ -10,7 +10,7 @@ ms.topic: conceptual
 author: stevestein
 ms.author: sstein
 ms.reviewer: carlrab
-ms.date: 03/10/2020
+ms.date: 04/30/2020
 ---
 # Scale single database resources in Azure SQL Database
 
@@ -42,14 +42,28 @@ Changing the service tier or compute size of mainly involves the service perform
 
 ## Latency 
 
-The estimated latency to change the service tier or rescale the compute size of a single database or elastic pool is parameterized as follows:
+The estimated latency to change the service tier, scale the compute size of a single database or elastic pool, move a database in/out of an elastic pool, or move a database between elastic pools is parameterized as follows:
 
 |Service tier|Basic single database,</br>Standard (S0-S1)|Basic elastic pool,</br>Standard (S2-S12), </br>Hyperscale, </br>General Purpose single database or elastic pool|Premium or Business Critical single database or elastic pool|
 |:---|:---|:---|:---|
 |**Basic single database,</br> Standard (S0-S1)**|&bull; &nbsp;Constant time latency independent of space used</br>&bull; &nbsp;Typically, less than 5 minutes|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|
 |**Basic elastic pool, </br>Standard (S2-S12), </br>Hyperscale, </br>General Purpose single database or elastic pool**|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|&bull; &nbsp;Constant time latency independent of space used</br>&bull; &nbsp;Typically, less than 5 minutes|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|
 |**Premium or Business Critical single database or elastic pool**|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|&bull; &nbsp;Latency proportional to database space used due to data copying</br>&bull; &nbsp;Typically, less than 1 minute per GB of space used|
 
+> [!NOTE]
+> Additionally, for Standard (S2-S12) and General Purpose databases, latency for moving a database in/out of an elastic pool or between elastic pools will be proportional to database size if the database is using Premium File Share ([PFS](https://docs.microsoft.com/azure/storage/files/storage-files-introduction)) storage.
+>
+> To determine if a database is using PFS storage, execute the following query in the context of the database. If the value in the AccountType column is `PremiumFileStorage`, the database is using PFS storage.
+ 
+```sql
+SELECT s.file_id,
+       s.type_desc,
+       s.name,
+       FILEPROPERTYEX(s.name, 'AccountType') AS AccountType
+FROM sys.database_files AS s
+WHERE s.type_desc IN ('ROWS', 'LOG');
+```
+
 > [!TIP]
 > To monitor in-progress operations, see: [Manage operations using the SQL REST API](https://docs.microsoft.com/rest/api/sql/operations/list), [Manage operations using CLI](/cli/azure/sql/db/op), [Monitor operations using T-SQL](/sql/relational-databases/system-dynamic-management-views/sys-dm-operation-status-azure-sql-database) and these two PowerShell commands: [Get-AzSqlDatabaseActivity](/powershell/module/az.sql/get-azsqldatabaseactivity) and [Stop-AzSqlDatabaseActivity](/powershell/module/az.sql/stop-azsqldatabaseactivity).