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Copy file name to clipboardExpand all lines: articles/storage/file-sync/file-sync-cloud-tiering-overview.md
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@@ -39,30 +39,30 @@ For more examples on how the date policy and volume free space policy work toget
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### Windows Server data deduplication
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Data deduplication is supported on volumes that have cloud tiering enabled beginning with Windows Server 2016. For details, see [Planning for an Azure File Sync deployment](file-sync-planning.md#data-deduplication).
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Data deduplication is supported on volumes that have cloud tiering enabled beginning with Windows Server 2016. For details, see [Plan for an Azure File Sync deployment](file-sync-planning.md#data-deduplication).
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### Cloud tiering heatmap
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Azure File Sync monitors file access (read and write operations) over time and assigns a heat score to every file based on how recently and frequently the file is accessed. It uses these scores to build a "heatmap" of your namespace on each server endpoint. This heatmap is a list of all syncing files in a location with cloud tiering enabled, ordered by their heat score. Frequently accessed files that were recently opened are considered hot, while files that were barely touched and haven't been accessed for some time are considered cool.
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To determine the relative position of an individual file in that heatmap, the system uses the maximum of its timestamps, in the following order: MAX (Last Access Time, Last Modified Time, Creation Time).
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Typically, last access time is tracked and available. However, when a new server endpoint is created with cloud tiering enabled, not enough time has passed to observe file access. If there's no valid last access time, the last modified time is used instead, to evaluate the relative position in the heatmap.
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Typically, last access time is tracked and available. However, when you create a new server endpoint with cloud tiering enabled, not enough time has passed to observe file access. If there's no valid last access time, the last modified time is used instead, to evaluate the relative position in the heatmap.
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The date policy works the same way. Without a last access time, the date policy will act on the last modified time. If that's unavailable, it will fall back to the create time of a file. Over time, the system will observe more file access requests and automatically start to use the self-tracked last access time.
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The date policy works the same way. Without a last access time, the date policy will act on the last modified time. If that's unavailable, it falls back to the create time of a file. Over time, the system will observe more file access requests and automatically start to use the self-tracked last access time.
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> [!NOTE]
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> Cloud tiering doesn't depend on the NTFS feature for tracking last access time. This NTFS feature is off by default. Due to performance considerations, we don't recommend that you manually enable this feature. Cloud tiering tracks last access time separately.
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### Considerations for choosing a cloud tiering policy
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Cold files that are less frequently accessed are best suited to be tiered files, as recalling data requires downloading from the cloud. Azure File Sync reserves 10% of total memory for persisting recalls to the disk. If 60% of this reserved memory is in use, the recalls won't be persisted to the disk. If a large number of tiered files are present on the system and a lot of access takes place, the system might hit a memory threshold. This can cause unexpected additional egress, I/O performance degradation, system slowness, and hangs.
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Cold files that are less frequently accessed are best suited to be tiered files, as recalling data requires downloading from the cloud. Azure File Sync reserves 10% of total memory for persisting recalls to the disk. If 60% of this reserved memory is in use, the recalls aren't persisted to the disk. If a large number of tiered files are present on the system and a lot of access takes place, the system might hit a memory threshold. This situation can cause unexpected additional egress, I/O performance degradation, system slowness, and hangs.
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### Proactive recalling
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When a file is created or modified, you can proactively recall a file to servers that you specify. Proactive recall makes the new or modified file readily available for consumption in each specified server.
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For example, a globally distributed company has branch offices in the US and India. In the morning in the US, information workers create a new folder and files for a brand new project, and work all day on it. Azure File Sync will sync folder and files to the Azure file share (cloud endpoint). Information workers in India will continue working on the project in their time zone. When they arrive in the morning, the local Azure File Sync enabled server in India needs to have these new files available locally so the India team can efficiently work off of a local cache. Enabling this mode tells the server to proactively recall the files as soon as they're changed or created in the Azure file share, improving file access times.
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For example, a globally distributed company has branch offices in the US and India. In the morning in the US, information workers create a new folder and files for a brand new project, and work all day on it. Azure File Sync syncs the folder and files to the Azure file share (cloud endpoint), which serves as the central hub between all registered servers. Information workers in India will continue working on the project in their time zone. When they arrive in the morning, the local Azure File Sync enabled server in India needs to have these new files available locally so the India team can efficiently work off of a local cache. Enabling proactive recall tells the server to download the files as soon as they're changed or created in the Azure file share, rather than waiting until a user tries to open them.
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If files recalled to the server aren't needed locally, then the unnecessary recall can increase your egress traffic and costs. Therefore, only enable proactive recalling when you know that pre-populating a server's cache with recent changes from the cloud will have a positive effect on users or applications using the files on that server.
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When the disk space runs out, Azure File Sync might not function correctly and can even become unusable. While it's not possible for Azure File Sync to completely prevent these occurrences, the low disk space mode (available in Azure File Sync agent versions starting from 15.1) is designed to prevent a server endpoint from reaching this situation and also help the server get out of it faster.
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For server endpoints with cloud tiering enabled, if the free space on the volume drops below the calculated threshold, then the volume is in low disk space mode.
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In low disk space mode, the Azure File Sync agent does two things differently:
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-**Proactive Tiering**: In this mode, the File Sync agent tiers files more proactively to the cloud. The sync agent checks for files to be tiered every minute instead of the normal frequency of every hour. Volume free space policy tiering typically doesn't happen during initial upload sync until the full upload is complete; however, in low disk space mode, tiering is enabled during the initial upload sync, and files will be considered for tiering once the individual file has been uploaded to the Azure file share.
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-**Proactive Tiering**: In this mode, the File Sync agent tiers files more proactively to the cloud. The sync agent checks for files to be tiered every minute instead of the normal frequency of every hour. Volume free space policy tiering typically doesn't happen during initial upload sync until the full upload is complete; however, in low disk space mode, tiering is enabled during the initial upload sync, and files will be considered for tiering once the individual file is uploaded to the Azure file share.
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-**Non-Persistent Recalls**: When a user opens a tiered file, files recalled from the Azure file share directly won't be persisted to the disk. Recalls initiated by the `Invoke-StorageSyncFileRecall` cmdlet are an exception to this rule and will be persisted to disk.
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Calculate the threshold by taking the minimum of the following three numbers:
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- 10% of volume size in GiB
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- 10% of volume size in GiB
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- Volume Free Space Policy in GiB
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- 20 GiB
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The primary cause of low disk mode is copying or moving large amounts of data to the disk where a tiering-enabled server endpoint is located.
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### How to get out of low disk space mode?
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Here are two ways to exit low disk mode on the server endpoint:
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1. Low disk mode will automatically switch to normal behavior by not persisting recalls and tiering files more frequently, without requiring any intervention.
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2. You can manually speed up the process by increasing the volume size or freeing up space outside the server endpoint.
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Low disk mode will automatically switch to normal behavior by not persisting recalls and tiering files more frequently, without requiring any intervention. You can manually speed up the process by increasing the volume size or freeing up space outside the server endpoint.
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### How to check if a server is in Low Disk Space mode?
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- If a server endpoint is in low disk mode, it is displayed in the Azure portal in the **cloud tiering health** section of the **Errors + troubleshooting** tab of the server endpoint.
Copy file name to clipboardExpand all lines: articles/storage/file-sync/file-sync-introduction.md
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@@ -4,34 +4,34 @@ description: Get an overview of Azure File Sync, a service that enables you to c
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author: khdownie
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ms.service: azure-file-storage
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ms.topic: overview
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ms.date: 06/04/2025
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ms.date: 04/09/2026
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ms.author: kendownie
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# Customer intent: "As an IT administrator looking to optimize file storage, I want to implement Azure File Sync so that I can centralize my file shares in the cloud while maintaining quick local access and ensuring data resilience across multiple sites."
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---
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# What is Azure File Sync?
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Azure File Sync is a service for centralizing an organization's file shares in Azure Files while keeping the flexibility, performance, and compatibility of a Windows file server.
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Azure File Sync is a service for centralizing an organization's file shares in Azure Files while keeping the flexibility, performance, and compatibility of an on-premises Windows file server. Azure File Sync uses an Azure file share as the central hub for your organization's file data. Each on-premises Windows Server that you register with Azure File Sync syncs its data to and from this Azure file share.
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Although you can opt to keep a full copy of your data locally, Azure File Sync can transform Windows Server into a quick cache of an Azure file share. You can use any protocol that's available on Windows Server to access your data locally, including Server Message Block (SMB), Network File System (NFS), and File Transfer Protocol over SSL/TLS (FTPS). You can have as many caches as you need across the world.
|[](https://www.youtube.com/watch?v=Zm2w8-TRn-o)|[](https://www.youtube.com/embed/6E2p28XwovU)|
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## Benefits of Azure File Sync
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### Cloud tiering
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When you enable cloud tiering, the files that you access most frequently are cached on your local server. The files that you access least frequently are tiered to the cloud. You can control how much local disk space is used for caching, and you can quickly recall tiered files on demand.
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When you enable cloud tiering, the files that you access most frequently are cached on your local Windows file server. The files that you access least frequently are tiered to an SMB Azure file share in the cloud. You can control how much local disk space is used for caching. The namespace is stored locally so the full file and folder structure is always visible and browseable. When a user opens a tiered file, Azure File Sync seamlessly recalls the file data from the Azure file share.
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Cloud tiering can help you cut costs, because you need to store only a fraction of your data on-premises. For more information, see [Cloud tiering overview](file-sync-cloud-tiering-overview.md).
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Cloud tiering reduces on-premises storage costs by allowing you to use a smaller local disk or keep more free space on existing disks, because only a fraction of your data needs to be stored locally. For more information, see [Cloud tiering overview](file-sync-cloud-tiering-overview.md).
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### Multiple-site access and sync
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Azure File Syncis ideal for distributed access scenarios. For each of your offices, you can provision a local Windows Server instance as part of your Azure File Sync deployment. Changes made to a server in one office automatically sync to the servers in all other offices.
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With Azure File Sync, changes made on any registered Windows server are first synced up to the Azure file share, and then synced down to the other servers, enabling multi-site access. Azure File Sync is ideal for distributed access scenarios because multiple offices can share the same set of files without having to connect directly to each other. For each of your offices, you can provision a local Windows Server as part of your Azure File Sync deployment. Changes made to a server in one office automatically sync to the servers in all other offices.
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### Business continuity and disaster recovery
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### Cloud-side backup
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Reduce your on-premises backup spending by taking centralized backups in the cloud via Azure Backup. SMB Azure file shares have native snapshot capabilities. You can automate the process by using Azure Backup to schedule your backups and manage their retention.
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Reduce your on-premises backup spending by taking centralized backups in the cloud via Azure Backup. Azure file shares have native snapshot capabilities. You can automate the process by using Azure Backup to schedule your backups and manage their retention.
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Azure Backup also integrates with your on-premises servers. When you restore to the cloud, the changes are automatically downloaded on your Windows Server instance.
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### Migration
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### Cloud migration
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Azure File Sync enables seamless migration of your on-premises file data to Azure Files. By syncing your existing file servers with Azure Files in the background, you can move data without disrupting users or changing access patterns. Your file structure and permissions remain intact, and applications continue to operate as expected.
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This ability can help you modernize infrastructure, consolidate storage, or retire aging hardware while ensuring continuous availability.
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## Training
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For self-paced training, see the following modules:
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-[Implement a hybrid file server infrastructure](/training/modules/implement-hybrid-file-server-infrastructure/)
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-[Extend your on-premises file share capacity using Azure File Sync](/training/modules/extend-share-capacity-with-azure-file-sync/)
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For self-paced training, see [Implement a hybrid file server infrastructure](/training/modules/implement-hybrid-file-server-infrastructure/).
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## Architecture
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-[Plan for an Azure File Sync deployment](file-sync-planning.md)
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