On-premises NAS migration to Azure File Sync

Summary — Migrate from NAS to a hybrid cloud deployment with Azure File Sync

What this guide covers

• Scenario: Migrate SMB file shares from Network Attached Storage (NAS) to a Windows Server, then use Azure File Sync to sync those folders to Azure file share(s) (hybrid cloud with on-premises caching).

• Key constraint: Azure File Sync works only with Direct Attached Storage (DAS) on Windows Server — it cannot sync directly from NAS. You must copy NAS data to a Windows Server first (for example, using Robocopy).

• Target outcome: Keep production data integrity and minimize downtime while enabling cloud tiering (local cache) via Azure File Sync.

Applies to

• SMB file shares on standard and premium Azure file shares (NFS is not supported in this scenario).

High-level migration overview

1

Plan mapping & capacity (Phase 1)

• Determine how many Azure file shares you need (one Windows Server can sync up to 30 Azure file shares).

• Options if >30 shares: group related shares under a common root folder, sync volume roots, or add more Windows Servers.

• Keep items per Azure file share well below absolute limits (recommended <20–30M items for performance).

• Create a mapping table (namespace mapping) to record which on-prem folders map to which Azure file shares.

2

Provision Windows Server (Phase 2)

• Deploy Windows Server 2019/2022 (VM or physical) and attach DAS.

• You can provision less local capacity if you use Azure File Sync cloud tiering, but then move data in batches (or use Robocopy /LFSM).

• Size CPU/RAM based on number of items to sync.

3

Deploy cloud resources (Phases 3–4)

• Create a Storage Sync Service in the Azure region that matches your resources.

• Provision storage accounts and Azure file shares per your mapping. Best practice: consider one file share per storage account for high-activity shares; low-activity shares can share accounts.

• Ensure redundancy and file share size settings meet your needs (100 TiB shares have limitations).

4

Install agent & register server (Phase 5)

• Install Azure File Sync agent on the Windows Server and register the server to the Storage Sync Service.

• Install required PowerShell modules (Install-Module -Name Az; Install-Module -Name Az.StorageSync).

• Configure proxy/firewall access if needed (see provided networking guidance).

5

Configure sync groups & server endpoints (Phase 6)

• Create a sync group per Azure file share; the Azure file share is the cloud endpoint.

• Add a server endpoint for each local folder you want to sync.

• Enable cloud tiering if local capacity < data size (set high temporarily during migration, e.g., 99% free space).

6

Copy data with Robocopy (Phase 7)

• Use Robocopy from NAS → Windows Server target folders that are server endpoints.

• Example command provided in the original article. Recommended switches and meanings are explained (e.g., /MT, /MIR, /B, /LFSM).

• Beware Robocopy can outpace cloud-tiering and fail with "volume full" — plan copies in batches or use /LFSM for tiered targets (with compatibility caveats).

7

Cut over users (Phase 8)

• Run initial RoboCopy, then repeat to catch deltas until a final acceptable downtime window.

• Quiesce users (prevent changes on NAS), run final Robocopy, create SMB shares on the Windows Server, and point clients/DFS to the new shares.

• After migration, reduce cloud tiering free-space policy to a long-term value (for example ~20%) across all sync groups.

Key considerations, tips, and troubleshooting

• Scale vector: number of items (files/folders) per share matters most — try to stay below recommended item counts for performance and management.

• Use namespace mapping and grouping to manage limits (30 shares per server, storage account performance limits).

• If Robocopy errors with "volume full", allow Azure File Sync cloud tiering to free space (it runs hourly), then resume the copy.

• Prefer Windows Server 2022; if using 2019, ensure patch KB5005103 or latest updates are applied for Robocopy fixes.

• After migration, verify cloud tiering settings across all sync groups to avoid unintended high free-space policies.

Helpful links (from the original article)

• Mapping/template download: https://download.microsoft.com/download/1/8/D/18DC8184-E7E2-45EF-823F-F8A36B9FF240/Azure%20File%20Sync%20-%20Namespace%20Mapping.xlsx

• Azure File Sync agent download: https://aka.ms/AFS/agent

• Azure File Sync planning and deployment docs (links preserved in original article)

Last updated in the source: 02/23/2024.