How do you migrate a file server to SharePoint Online?

Key facts

• Do not lift and shift drive letters; redesign shares into sites and libraries by team or function.
• SharePoint Migration Tool suits smaller jobs; Migration Manager runs agents for larger, parallel jobs.
• Pre-scans catch long paths, invalid characters, very large files and blocked file types before cutover.
• Map permissions to Microsoft 365 or Entra groups, not to individual users.
• Set old shares to read-only at cutover rather than deleting them right away.

Step 1: Assess what is on the file server

Start with numbers. Measure total size, file count, folder depth, file types, last-modified dates and owners for each share. Most file servers hold a large share of data no one has opened in years, plus duplicates, installers, backups and personal files.

SharePoint Migration Tool and Migration Manager both include scan options that flag issues. Look for paths that will exceed SharePoint path limits after the site URL is added, characters SharePoint does not allow, files above the upload size limit, and file types blocked by policy. Also flag databases such as Access files and PST files, which do not belong in a synced library.

Step 2: Clean up and decide what moves

Agree on rules with department owners before any copy job runs. A common approach is to move active content, archive stale content to cheaper storage, and delete obvious junk with sign-off.

• Set an age cutoff for archive, for example content untouched for several years, adjusted for legal holds and retention needs.
• Remove duplicates, installers, temp files and backups.
• Flatten deep folder trees that will break path limits.
• Name an owner for every share; unowned data is archived, not migrated.
• Move personal home drives to each user's OneDrive, not to a shared site.

Step 3: Design sites and libraries

A file server has drive letters and one big tree. SharePoint works better with many smaller sites, each with its own owners and permissions. Map each department or long-running team to a Teams-connected site, and map company-wide reference content such as policies and templates to a communication site.

Keep libraries reasonably sized and avoid breaking permission inheritance on individual folders. If a folder needs different access, it usually deserves its own library or site. Plan metadata or views only where people will use them; most teams just need a clean folder structure.

Step 4: Choose the tool and run the copy

SharePoint Migration Tool is free and runs on a single machine, which suits smaller servers. Migration Manager, in the SharePoint admin center, lets you install agents on several machines and run many jobs in parallel from one console, which suits larger servers and multiple sites. Third-party tools add features such as detailed permission mapping, scheduling and reporting.

Run the copy in passes. The first pass moves the bulk of data while users keep working on the file server. Later incremental passes pick up only changed files. On cutover day, run a final delta, then set the source shares to read-only.

Step 5: Cut over and support users

Tell users where each share now lives and how to reach it: through the Teams Files tab, the SharePoint site, or by syncing a library with OneDrive. Remove old drive mappings by Group Policy or Intune, and replace them with sync or shortcuts where needed.

Watch for apps that open files by UNC path, macros and linked spreadsheets that point to the old server, and scanners that save to a share. Each needs a new target. Keep the read-only source for an agreed period, then archive and retire the server.

How Accred Consulting approaches it

Accred Consulting runs a file assessment during discovery, measuring size, age, path issues and permissions, and agrees on cleanup rules with department owners. The Proposal sets the site design, tooling, fixed price and timeline. In one SharePoint engagement for about 240 users, about 1.8 TB was assessed and moved into 11 governed sites over 9 weeks. US-based specialists run pre-stage and delta passes, test with pilot users, and support cutover. Handover includes documentation of site owners, permissions and the archive plan.

Track record: 400+ client projects, 2,000+ migration workstreams and 150,000+ users migrated by a US-based team. Company facts · Case studies

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