Decide whether SharePoint is the right home
SharePoint suits ordinary office documents: Word, Excel, PDFs, images and the general paperwork of a business. It is less suited to some workloads that often sit on a file server, such as an accounting package's shared database, large CAD assemblies with linked references, video editing projects or line-of-business software that expects a mapped drive letter. Those need checking with the software vendor before anything moves.
Start with an inventory. List the top-level folders, their size, how many files they hold and who uses them. Flag anything that is a program's data folder rather than documents. It is common to end up with most of the drive going to SharePoint, one or two folders staying on a small server or NAS, and a pile of old material going to an archive.
Clean up before you move anything
Most shared drives carry years of duplicates, abandoned folders and personal files that never belonged there. Copying all of that into SharePoint just moves the mess somewhere more expensive to search. Sort folders by last modified date and look hard at anything untouched for several years. Old material can go to a read-only archive library rather than the main working area.
Look for the problems that break migrations: very long folder paths, file names with characters SharePoint dislikes, huge numbers of tiny files, and old Office formats that may be better converted. Remove personal music and photo collections and talk to the owners about them first. This step usually takes longer than the copy, and it is where the real benefit of the move comes from.
Map old folders to new libraries
Build a simple spreadsheet with each old top-level folder in one column and its new site and library in the next. Use the permission groups as your guide: anything only finance should see goes to the finance site, anything company-wide goes to the shared site. Where an old folder mixes sensitive and general material, split it during the clean-up rather than after.
Resist the urge to recreate the exact old structure inside one giant library. One enormous library with everything in it brings the old problems with it, including slow sync and confusing permissions. Several focused libraries are easier to sync selectively, easier to secure and easier for staff to understand. Share the map with staff before cutover so the new locations are not a surprise.
Run the migration in passes
Microsoft provides free migration tools that copy from a file share into SharePoint while keeping created and modified dates, and several paid tools add reporting and scheduling. Whichever you use, do a first bulk copy while people keep working on the old drive. That pass can take days for a large drive on a modest internet connection, so plan around your upload speed.
Then pick a cutover time, usually after close of business on a Friday. Set the old share to read-only, run a final pass that copies only what changed since the first one, check the reports for failures and fix them. On Monday staff open the new libraries, and nobody has been locked out of their files for more than an evening.
Setting up laptops and getting staff across
Decide how people will reach the new libraries. Adding shortcuts to their OneDrive is often simpler than syncing many separate libraries, and Files On-Demand means the files show in File Explorer without filling the laptop's drive. Do not tell everyone to sync every library on day one, because a full sync of a large drive on every machine at once can saturate your internet connection.
Give staff a single page showing where each old folder now lives, with links. Expect a week of questions about where things went and about links in old documents and email that pointed to the S drive. Spreadsheets that link to other spreadsheets by drive path will need their links updated, and it is worth finding the important ones before cutover.
After cutover
Keep the old drive read-only for four to six weeks so anyone who discovers a missing file can find it. Then take a final backup of it, store that somewhere safe and switch the share off. If the server has nothing else to do, plan its retirement, including secure wiping of the disks before disposal.
Finally, sort out backup for the new home. SharePoint has version history and a recycle bin, but they are not the same as an independent backup, so add a Microsoft 365 backup that covers SharePoint and OneDrive and test a restore. Office IT quotes migrations like this in writing first, with the folder map agreed before any data moves.
In short
- Check for application data folders that should not go to SharePoint.
- Clean up and archive before copying; the clean-up is where the value is.
- Map old folders to new libraries along permission lines.
- Copy in a bulk pass, then a short read-only cutover and final pass.
- Keep the old drive read-only for a few weeks, then back up and retire it.