File server to SharePoint Online, step by step
Copying files is the easy part. What breaks a file server migration is everything around them: permissions SharePoint cannot reproduce one to one, paths it rejects, folders nobody owns, and a cutover while people keep working. These are the steps that matter and the limits to check before you start.
SharePoint limits to check first
| Path length | 400 characters for the full decoded path, file name included. |
|---|---|
| Characters | Names cannot contain " * : < > ? / \ | |
| Blocked names | .lock, CON, PRN, AUX, NUL, COM0 to COM9, LPT0 to LPT9, _vti_, desktop.ini, and any name that starts with ~$. |
| File size | 250 GB per file. |
| Unique permissions | Up to 50,000 per list or library, and Microsoft recommends staying under 5,000. A folder with more than 100,000 items cannot get its own permissions. |
Source: Microsoft, as published in October 2026. SharePoint limits and Restrictions and limitations in OneDrive and SharePoint
The migration, step by step
- 1
Take an inventory without changing anything
Size and number of files, who has access to what, paths and names SharePoint will reject, duplicates, abandoned folders and files open right now. Nothing gets decided before this.
- 2
Decide what moves, and where
A file server holds years of habits. The migration is the moment to archive what nobody uses and give the rest a structure: which site, which library, which folders.
- 3
Map the permissions, never wider
NTFS permissions do not translate one to one: groups, inheritance, "Everyone", deny entries. The safe rule is that nobody ends up seeing more than before. What cannot be reproduced exactly waits for a decision.
- 4
Let the data owners decide
Whether a team should still see Payroll is a business question, not an IT one. Ask the owner, and keep a record of who decided.
- 5
Migrate in incremental passes
Copy while the server is still in use, then repeat: each pass copies only what is new or changed. Stay within Microsoft’s throttling so the rest of the company is not slowed down.
- 6
Verify every file, then cut over
Counting files proves little. Compare each one with its original, read dates, authors and permissions back from SharePoint, and keep the record. Then make the old share read-only and move people over.
How Sendero does it
Sendero runs these steps with an agent inside your network. It analyzes without writing anything, explains what it found, proposes the plan as rules you can read, asks the data owners, migrates once someone with authority approves, and checks every file against the original. Your files go from your servers to your Microsoft 365, never through Montecode.
Questions
Can I keep NTFS permissions when moving to SharePoint Online?
Mostly, when each group or user has an equivalent in Microsoft 365. Deny entries and broad grants such as "Everyone" have no exact equivalent: Sendero holds those items until an owner decides, so nothing ends up more open than before.
What happens to paths longer than 400 characters?
SharePoint rejects them, so they have to be shortened or reorganized. Sendero lists them in the analysis, fixes names SharePoint refuses and keeps the list of changes for users; relocation rules can move deep folders to a shorter path, with a preview.
Do people have to stop working during the migration?
No. Incremental passes copy while the server is in use; only the last pass and the switch need a short window.
How long does it take?
It depends on the volume and on the limits Microsoft applies to your tenant. The first analysis estimates it with your real data.