File server to SharePoint migration: a step-by-step checklist with Microsoft's real limits
File server to SharePoint migration in 7 steps: long paths, permissions, sync and Migration Manager, with Microsoft's current limits checked October 2026.
A file server to SharePoint migration goes best in seven steps once you've ruled out what shouldn't move: inventory and clean up, fix long paths and blocked names, redesign permissions, plan sites and libraries, plan sync, choose the migration tool, then pilot and cut over to a read-only old share. Every limit below was checked against Microsoft's documentation on 15 October 2026.
Microsoft revises these limits, so check the date on any guide. Ours come from Microsoft's SharePoint limits page (last updated in October 2026) and the documentation linked below.
What are Microsoft's SharePoint limits for a file server migration?
| Limit | Microsoft's figure | What it means for you |
|---|---|---|
| Path length | 400 characters for the entire decoded path, including the file name | Deep folder trees need flattening |
| File size | 250 GB per file | Rarely an issue outside video |
| Breaking inheritance | Not possible on a list, library or folder with more than 100,000 items | Set access before content lands |
| Unique permissions | 50,000 per list or library supported; 5,000 recommended | Folder-by-folder access doesn't scale |
| OneDrive sync | No more than 300,000 files recommended per library, or across everything a person syncs | Archives should be browsed, not synced |
| Storage (Business plans) | 1 TB per organisation plus 10 GB per licence; 25 TB per site | Big servers may need clean-up or extra storage |
| Structure | Separate sites organised into hubs, not subsites (a recommendation) | Plan a flat set of sites |
Should your file server move to SharePoint at all?
For everyday documents, usually yes: co-authoring, version history, access from anywhere with multi-factor sign-in, and no file server to patch. Three kinds of content need a different plan, so find them first.
Access databases.
Microsoft says to avoid opening an Access database from OneDrive or a SharePoint library, because several people opening it may create multiple copies. Move the data to a proper database or SharePoint list, or keep it on a server.
Large CAD and video projects.
Big files that link to other files by path can misbehave under OneDrive sync. Ask your software vendor first.
Software that expects a drive letter.
Practice management and accounting systems that keep data on a mapped drive usually won't run from a SharePoint library; they need a server, on-premises or an Azure virtual machine.
Timing matters too: Windows Server 2016 extended support ends in January 2027, and moving shared documents to SharePoint shrinks whatever replaces an old server.
Step 1: Inventory and clean up
List every share and top-level folder with its size, last change date and owner: the person who decides what stays and who sees it. Unclaimed folders are archive candidates. Delete duplicates, old installers and decade-old scans before you copy.
Size matters because SharePoint storage is pooled. Microsoft 365 Business plans include 1 TB per organisation plus 10 GB per licence, so a business with 20 licences has about 1.2 TB across all its sites; OneDrive is counted separately. Microsoft warns a tenant running over its limit risks going read-only. Personal home drives belong in each person's OneDrive, and Microsoft's migration overview points to Known Folder Move for Windows folders such as Desktop, Documents and Pictures.
Step 2: Scan for long paths and blocked file names
Migration Manager's scan counts the tenant address and site in its maximum path length, so keep site and library names short. The practical ceiling is lower still: Microsoft's path length guide says the Word, Excel and PowerPoint desktop apps on Windows can't open a file whose full path exceeds 260 characters, even if it's stored locally, and syncing adds your Windows user folder and organisation name to the front of every path. Flatten deep trees and shorten long folder names.
Then check names. OneDrive and SharePoint don't allow the characters " * : < > ? / | or a backslash, leading or trailing spaces, names such as CON, PRN, AUX, NUL, COM0 to COM9 and LPT0 to LPT9, .lock, desktop.ini, anything containing _vti_, or names starting with ~$. Switch on Migration Manager's Only perform scanning setting for a pre-migration check: the scan's readiness warnings flag problems such as invalid characters before anything is copied.
Step 3: Redesign permissions instead of copying them
Years of "just give Sarah that folder" leave permissions nobody can explain, and SharePoint isn't built for them. Microsoft supports 50,000 unique permissions in a list or library but recommends 5,000, and once a list, library or folder holds more than 100,000 items you can't break or restore its inheritance. Give each group needing different access its own site, set permissions through groups, and keep folder exceptions rare. Migration Manager can preserve file share permissions, which helps only when they're already tidy.
Copilot raises the stakes. Microsoft says Copilot only surfaces organisational data a person can already view, so whatever sits in an over-shared folder can turn up for anyone who asks Copilot the right question. If Microsoft Copilot is on your roadmap, fix access now.
Step 4: Plan sites and libraries with hubs, not subsites
Microsoft recommends separate sites organised into hubs rather than subsites. Its hub planning guide explains why: subsites are built into the URL, so reorganising the business breaks the relationships between them, while joining a site to a hub doesn't change its permissions. A useful rule: a different audience means a different site; the same audience with different content means a different library.
| On the file server | Usually moves to |
|---|---|
| Department shares (Accounts, HR) | A private site per department |
| Templates, policies and forms | A communication site everyone reads |
| Projects or clients | A projects site, or a team in Microsoft Teams |
| Home drives | Each person's OneDrive |
| Old archives | An archive library, browsed rather than synced |
| Databases and application data | A server or Azure, not SharePoint |
Step 5: Plan sync before anyone presses Sync
Staff will want files in File Explorer, meaning OneDrive sync. Microsoft recommends syncing no more than 300,000 files in a library, and the same slowdowns appear once a person's synced libraries pass 300,000 items in total, shortcut folders included. Sync only the libraries people use daily; open archives in the browser or Teams. Microsoft now recommends Add shortcut to My files as the most versatile option where it's available, and no longer recommends the View in File Explorer command. Our Microsoft 365 time-savers cover sharing links instead of attachments.
Step 6: Choose the migration tool
- Migration Manager runs from the SharePoint admin centre and copies through agents on one or more Windows machines. Microsoft's prerequisites: the source server must support SMB 2.0 or later, you need Global admin or SharePoint admin rights, and Windows credentials with read access to the shares. Each agent machine needs Windows 10 or Windows Server 2016 or later, at least 8 GB of RAM (16 GB recommended) and 150 GB free on a solid-state disk, per the system requirements. The newer Migration Administrator role can manage file share migrations, though installing an agent needs a SharePoint Administrator sign-in.
- The SharePoint Migration Tool (SPMT) is a free Microsoft tool you install on a computer; it handles file shares too.
Dragging files into a synced library suits one person's documents, but with no scan, report or permission mapping it's the wrong way to move a whole server.
Step 7: Pilot, cut over, then set the old share to read-only
Pilot one team.
Migrate one department, let them work from SharePoint for a couple of weeks, and read the failure reports.
Copy the bulk while staff keep using the server.
Microsoft strongly recommends not renaming or moving migrated files before the final migration, because files get overwritten, so leave the SharePoint copies alone until cut-over.
Run incremental passes.
Migration Manager's delta sync copies only new or changed files; full incremental compares every file, so it catches files added with a modified date older than the last pass. Files deleted from the server after the first copy stay in SharePoint, which is why clean-up comes first.
Cut over.
Run the final pass at a quiet time, then set the old shares to read-only. Migration copies files and doesn't delete the source, so skip this and you'll have two versions of the truth.
Retire the drive letters.
Remove mapped drives from logon scripts and device policies, keep the read-only server for an agreed period, then decommission it.
SharePoint isn't a backup. Deleted items can be restored from the recycle bin for 93 days, and ransomware on a synced laptop can push encrypted files into a library. Build an independent backup into the project; it's part of our backup and disaster recovery service.
When should you call someone in?
A small office with one tidy share can run this itself. Get help when several apply: more than a terabyte of data, years of folder-level permissions, Access databases or line-of-business software on the same server, a server nearing end of support, or client and patient records. Key IT runs SharePoint migrations for Melbourne businesses as part of our cloud migration services, from Greensborough and remotely across regional Victoria, then looks after the result through Microsoft 365 management.
Frequently asked questions
How long does a file server to SharePoint migration take?
It depends on data volume, clean-up and upload speed, and planning often takes longer than the copy itself. A small, tidy share can move quickly; a multi-terabyte server with tangled permissions needs a staged project. Start with a scan-only pass in Migration Manager: its file counts, sizes and problem paths are what an honest timeline is built on.
Can we keep our mapped drive letters after moving to SharePoint?
Not in the same way. SharePoint libraries appear in File Explorer through OneDrive, by syncing a library or adding a shortcut to My files, and show up as folders rather than as an S: or P: drive. If software genuinely needs a drive letter, its data should stay on a server.
Will our folder permissions come across in the migration?
They can. Migration Manager can preserve file share permissions, mapping on-premises accounts to Microsoft 365 users through Microsoft Entra ID or a mapping file. But Microsoft recommends no more than 5,000 unique permissions per library, and folder-by-folder access is hard to manage, so most businesses do better rebuilding access around sites and groups.
Is SharePoint a backup for our files?
No. Version history and the recycle bin help undo mistakes, but deleted items leave the recycle bin after 93 days, and ransomware or a compromised account can damage SharePoint files as easily as files on a server. Keep an independent, immutable backup of SharePoint and OneDrive, and test a restore before you retire the old server.
Should our files go to SharePoint, Teams or OneDrive?
Shared business files go to SharePoint, and the files on a team's Files tab in Microsoft Teams are stored in a SharePoint site, so they aren't competing choices. Personal working files belong in OneDrive. A simple test: if a colleague would need the file while its author is on leave, it belongs in SharePoint.
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