Merge pull request #274465 from khdownie/patch-1

Update file-sync-choose-cloud-tiering-policies.md

Author: prmerger-automator[bot]

articles/storage/file-sync/file-sync-choose-cloud-tiering-policies.md

@@ -55,6 +55,9 @@ The reason for the absolute minimum is due to the way NTFS stores extremely smal
 
 Generally, when you enable cloud tiering on a server endpoint, you should create one local virtual drive for each individual server endpoint. Isolating the server endpoint makes it easier to understand how cloud tiering works and adjust your policies accordingly. However, Azure File Sync works even if you have multiple server endpoints on the same drive, for details see the [Multiple server endpoints on local volume](file-sync-cloud-tiering-policy.md#multiple-server-endpoints-on-a-local-volume) section. We also recommend that when you first enable cloud tiering, you keep the date policy disabled and volume free space policy at around 10% to 20%. For most file server volumes, 20% volume free space is usually the best option.
 
+> [!NOTE]
+> In some migration scenarios, if you provisioned less storage on your Windows Server instance than your source, you can temporarily set volume free space to 99% during the migration to tier files to the cloud, and then set it to a more useful level after the migration is complete.
+
 For simplicity and to have a clear understanding of how items will be tiered, we recommend you primarily adjust your volume free space policy and keep your date policy disabled unless needed. We recommend this because most customers find it valuable to fill the local cache with as many hot files as possible and tier the rest to the cloud. However, the date policy may be beneficial if you want to proactively free up local disk space and you know files in that server endpoint accessed after the number of days specified in your date policy don't need to be kept locally. Setting the date policy frees up valuable local disk capacity for other endpoints on the same volume to cache more of their files.
 
 After setting your policies, monitor egress and adjust both policies accordingly. We recommend looking at the **cloud tiering recall size** and **cloud tiering recall size by application** metrics in Azure Monitor. We also recommend monitoring the cache hit rate for the server endpoint to determine the percentage of opened files that are already in the local cache. To learn how to monitor egress, see [Monitor cloud tiering](file-sync-monitor-cloud-tiering.md).