How to move a file server to SharePoint, and what breaks

Most small offices still have one. A server in the comms cupboard, or a NAS on a shelf, holding an S: drive that everybody has used since before half the staff joined. Folders inside folders inside a folder called OLD. Permissions that one person set up years ago and nobody has dared touch since.

Then something forces the question. Windows Server 2016 stops getting security updates on 12 January 2027, the NAS starts making a noise, or someone asks for the fourth time why they can't open the drive from home. So the search goes in: how do I move our file server to SharePoint?

Copying the files is the easy part. Microsoft provides the tools. Whether Monday morning goes well depends on what doesn't copy cleanly: names SharePoint won't accept, paths too long to store, permissions that don't translate, and a few files that should never have lived on a shared drive at all. Here's the order we'd tackle it in.

Does everything on a file server belong in SharePoint?

Documents do. Word files, spreadsheets, PDFs, drawings, photos. SharePoint takes individual files up to 250 GB, and Microsoft's SharePoint Migration Tool lists local and network file shares as a supported source.

Not everything on the S: drive is a document, though, and three kinds of file need a decision before anything moves.

Access databases come first. Microsoft's own Access guidance says you can save a database to OneDrive or a SharePoint library but recommends you avoid opening it from there. If more than one person opens it, multiple copies may be created and, in Microsoft's words, some unexpected behaviours may occur. Split databases are included in that.

Then there's anything an application opens across the network: an accounts package, a practice-management system, a CAD library. Those were built for a mapped drive and a server that's always on. Ask the vendor what they support before you touch the data folder. Some will tell you their own hosted version is the answer, and it usually is.

The third group is small and annoying. OneNote notebooks keep their own sync, and Microsoft says moving an existing notebook into a synced folder without going through OneNote isn't supported (notebooks in OneDrive or SharePoint are also capped at 2 GB). Outlook PST files sync less often than other files, and Outlook can show errors once a PST isn't where it expects. We'd import old PSTs into the mailbox or archive them rather than sync them.

If the server also runs a print queue, a database server or the domain itself, that's a bigger job, and our Windows Server 2016 guide works through what a server is actually doing before anything is retired. This article is about the files.

SPMT or Migration Manager?

Microsoft gives you two tools. They copy the same way. The difference is scale.

The SharePoint Migration Tool, SPMT, is a desktop application Microsoft describes as free. You install it on one machine that can see the share, sign in to the tenant, point it at a source folder and a destination library, and it scans, packages, uploads and imports. It needs a working folder with at least 150 GB free, which catches people out on a laptop.

Migration Manager lives in the SharePoint admin centre. You install a small agent on one or more machines near the data, and tasks go to whichever agent is free, so adding machines adds speed. The prerequisites ask for Windows Server 2016 or later, or Windows 10, with 8 GB of RAM as a minimum and 16 GB recommended, 150 GB of free SSD space, and a source that supports SMB 2.0 or higher. A very old NAS sometimes doesn't.

Both want admin rights in Microsoft 365 and read access to the share. For a ten-person office with a couple of hundred gigabytes, SPMT on one PC is plenty. We reach for Migration Manager when the data runs into terabytes or sits on more than one box.

Run a scan before you move anything

SPMT has a setting called Only perform scanning. Turn it on, point it at the whole share and read the report. It turns a vague worry into a list, and the list nearly always falls into the next four sections.

Names SharePoint won't accept

Microsoft's restrictions page lists the characters that aren't allowed in OneDrive for work or school or SharePoint: " * : < > ? / \ and |. Windows already refuses most of those, so on a Windows server they're rarely the problem. The ones that bite are the rest of the list.

No leading or trailing spaces, which Mac users create without noticing. None of these names, anywhere: .lock, CON, PRN, AUX, NUL, COM0 to COM9, LPT0 to LPT9 and desktop.ini. Nothing beginning with ~$, which is every lock file Word and Excel ever left behind after a crash. And _vti_ can't appear anywhere in a name. Some tenants still don't support # and % either, so "Quote #2.docx" is a real problem in a real office.

SPMT gives you a choice. With Replace invalid filename characters switched on, it swaps each bad character for one you pick. With it off, it skips the file. Skipping sounds safer. It isn't, because Microsoft's settings page warns that a package generating more than 100 errors at the destination gets blocked, valid files and all. We replace, and we keep the report, so whoever goes looking for "Quote #2" can find "Quote _2".

The 400-character path

This is the one that hurts. Microsoft's SharePoint limits cap the entire decoded path, folder names and file name together, at 400 characters.

Plenty, you'd think. File servers grow sideways for years, though. Clients, then Current, then the client's full company name, then the year, then the job address, then Drawings, then "Revisions from architect", then Superseded, then a file name that repeats half the folder names because somebody once emailed it out of context. Every move to a new folder made sense on the day. Together they add up to a path nobody could read aloud.

No tool setting fixes this. The structure has to change before the move, not after it. Give each department or client group its own library, so every path starts shorter, and keep to two or three levels of folders inside it. Search works in SharePoint in a way it never did on a file share, which is what makes a flatter structure bearable. This is the planning our cloud and Microsoft 365 page means by mapping what you have first, and honestly it's most of the job.

It's also far cheaper to do on the server. Microsoft's limits page caps a single move or copy between SharePoint sites at 100 GB and 30,000 files, so reorganising after the migration means doing it in pieces.

Permissions won't translate the way you hope

SPMT has a setting called Preserve file share permissions, and automatic user mapping is on by default, matching on-premises accounts to Microsoft Entra ID users where it can. So the tool will try. Whether you want it to is another matter.

Ten years of file-server permissions usually means folders shared with named people, some of whom left in 2019, plus at least one folder where Everyone has full control and nobody remembers why. Copy that faithfully and you've moved the mess somewhere it's easier to search. That matters more than it used to. Microsoft Copilot answers from anything a user can open, which we covered in our Copilot readiness guide.

SharePoint has hard limits here too. Once a library or folder holds more than 100,000 items, you can't break permission inheritance on it at all. Unique permissions are supported up to 50,000 items in a library, but Microsoft's recommended general limit is 5,000. A share with a different permission on every client folder can get there faster than you'd think.

Our default is permissions at site or library level, given through Microsoft 365 groups, with very few exceptions inside a library. If HR needs privacy, HR gets its own site. It's easier to explain to a new starter, and much easier to check a year later. Sharing with people outside the business is a separate set of switches, covered in how to restrict external sharing.

How much storage you actually get

On Microsoft 365 Business Basic, Standard and Premium, SharePoint storage is 1 TB for the organisation plus 10 GB per licence. Twelve users gets roughly 1.12 TB, shared across every site. Each person's OneDrive is separate and doesn't count.

The limits page is blunt about going over. A tenant that keeps running above its storage can be put into read-only mode until usage drops or more is bought, and site recycle bins count towards the total.

So measure the share before planning anything. If the server holds 1.6 TB and the tenant has 1.1, then either the archive goes somewhere else, or you buy extra storage from Microsoft, or a good deal of it gets deleted. Any of the three is fine. Finding out on day two isn't.

Sync is what staff actually notice

Nobody in the office cares where the files live. They care that the S: drive has gone. The OneDrive sync app replaces it, putting the library in File Explorer under your organisation's name, and Files On-Demand lets files sit there online-only until someone opens one.

There's a ceiling. Microsoft recommends syncing no more than 300,000 items in total across everything a user syncs, because performance suffers above that even when not every file is downloaded. Shortcut folders count. A public preview raising it to 1,000,000 started rolling out on 22 April 2026, but it needs the Insider build and doesn't support virtual desktops, so we still plan to 300,000.

Two habits keep people under it. Sync the libraries they use every day, not the archive. And for the rest, use Add shortcut to My files, which puts a single folder into their OneDrive rather than a whole library.

Cutover without losing Friday's work

The pattern is simple: copy everything early, let people carry on working on the server, then move only what changed. SPMT supports this directly, because a saved task can be rerun later and moves only new or updated files.

In practice the first pass runs midweek, and on a big share it can take a day or two. The people who own each folder spot-check it. Then on the agreed evening the share goes read-only so nothing new lands there, the incremental pass runs, sync gets switched on for everyone, and the old server stays up, read-only, for a few weeks. Somebody always finds a folder they're sure was on it.

Two settings are worth knowing about before that first pass. Hidden files aren't migrated unless Include hidden files is switched on. And you can migrate only files modified after a date you choose, if the business has decided that anything nobody touched since 2015 goes to an archive instead of the new library. That decision belongs to whoever runs the business, not to us.

What it costs with us

File migrations are quoted per project, because the size of the share, the state of its permissions and the number of oddities change the job more than the headcount does. The unit rates are published, so you can check our sums. Work outside a plan is £86 an hour for managed clients and £126 without a plan, £167 out of hours with a two-hour minimum, and an on-site day is £855. Mailboxes moving at the same time are £77 each, which is the job described in our Microsoft 365 migration guide.

Microsoft 365 licences, and any extra SharePoint storage, are supplied at list price with no markup. If the old server stays on for a while, it can sit under server management at £162 a month until it's switched off.

And SharePoint isn't a backup. Microsoft looks after the platform; the files are yours to protect, which we went into in whether Microsoft 365 backs up your data. Managed backup with tested restores comes with the Professional plan at £77 per user per month. All prices on the pricing page exclude VAT.

Before you book a date

Measure the share: total size, number of items, and the longest paths. Find the Access databases, PSTs, OneNote notebooks and application data folders, and decide what happens to each one. Draw the new structure on paper, with who can open what. Run a scan-only pass and read every error. Check the tenant's storage against the share. Then pick the evening. If you'd like someone else to look first, the free IT health check is where we start.