Migration Overview for SMB Azure File Shares
This article explains the core concepts and guidance for migrating SMB file shares to Azure file shares. It covers migration goals, preserving file fidelity, planning phases (discovery and assessment), provisioning Azure storage, networking and authentication considerations, recommended migration tools and helper tools, and where to find migration guides for common source systems.
Key points
Goal: Move file data into Azure file shares while preserving data integrity and minimizing downtime.
Targets:
Hybrid deployment: Azure Files + Azure File Sync (keeps on-premises cache).
Cloud-only deployment: Azure Files in the cloud (no local cache).
File fidelity: Migrations should preserve the data stream and supported file metadata (attributes, NTFS ACLs, timestamps). Alternative data streams cannot be stored on Azure file shares (they’re preserved only when using Azure File Sync).
Identity/access: Azure Files supports AD/Entra DS identity-based authentication and native NTFS ACLs; set root ACLs before large copies to avoid long propagation delays.
Planning: Discovery (inventory shares, size, dependencies) then assessment (choose storage type, region, redundancy, and networking/authentication strategy).
Storage deployment: Decide on storage account layout (shared pool vs single-share-per-account for heavy workloads) and redundancy. See Create an SMB file share.
Networking & access: Plan SMB routing (public/private endpoints), join storage accounts to AD if using identity-based auth, configure share-level and file/folder ACLs, and consider DFS-Namespaces to preserve share addresses.
Recommended tools: Azure Data Box, RoboCopy, Azure File Sync, Storage Migration Service, and Data Box Disk (note limitations). AzCopy and Azure Storage Explorer have limitations for full fidelity; Azure Data Factory does not copy metadata.
Helper tools: RoboCopy (built-in Windows utility) and TreeSize (to understand item counts for Azure File Sync sizing).
Important
If you're migrating on-premises file servers to Azure Files, set the ACLs for the root directory of the file share before copying a large number of files — changing root ACLs after a large migration can take a long time to propagate.
Supported metadata (summary)
Directory structure: preservable.
Access permissions: Windows ACLs supported; preserve owner SID, group SID, DACLs, SACLs.
Timestamps: Creation, Change, Modified can be preserved. LastAccessTime is not currently supported on the target (Azure Files will return its value if requested but LastModifiedTime isn't updated on read).
File attributes: Read-only, hidden, archive flags can be preserved.
Alternative data streams: Not stored on Azure file shares (preserved only when using Azure File Sync).
How to use the migration guides
Recommended tool guidance (short)
Full-fidelity/recommended: Azure Data Box, RoboCopy, Azure File Sync, Storage Migration Service, Data Box (copy service). These preserve metadata where supported.
Use with caution: AzCopy (some fidelity loss; up to 10M files per job).
Not recommended for full fidelity: Azure Storage Explorer (loses ACLs), Azure Data Factory (doesn't copy metadata).
Helper tools
RoboCopy: Good for mirroring and iterative copies to reduce downtime (e.g., robocopy /MIR).
TreeSize: Useful to estimate item counts (files/folders) for Azure File Sync sizing; tested version 4.4.1.
Where to read more (selected links)
Azure file shares: https://docs.azure.cn/en-us/storage/files/storage-files-introduction
Azure File Sync planning: https://docs.azure.cn/en-us/storage/file-sync/file-sync-planning
Create an SMB file share: https://docs.azure.cn/en-us/storage/files/storage-how-to-create-file-share
Azure Data Box: https://docs.azure.cn/en-us/databox/data-box-overview?pivots=dbx-ng
RoboCopy docs: https://learn.microsoft.com/windows-server/administration/windows-commands/robocopy
Last updated: 09/02/2025
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