What is OneDrive?

OneDrive is the personal cloud file storage that comes with every Microsoft 365 user account — typically 1 TB per user on business plans, more on some enterprise SKUs. It's the least glamorous service in the suite and one of the most load-bearing: it's where drafts live, where the sync client puts your Desktop and Documents, where "can you give me access to that file?" starts, and — handled well — the quiet end of laptop backup as a problem category.

Under the surface, OneDrive is SharePoint: each user's OneDrive is a personal SharePoint site with a friendlier interface. That single fact explains most of its behaviour — versioning, sharing, retention, and admin controls all inherit from the SharePoint platform underneath.

What OneDrive actually does

• Personal cloud storage for your own working files: drafts, notes, screenshots, personal copies of shared material.
• Sync — the OneDrive client for Windows and macOS mirrors cloud files to the device. Files On-Demand keeps placeholders locally and downloads content only when a file is opened, which is why a 1 TB OneDrive fits on a 256 GB laptop. How the client actually behaves — and misbehaves — is in the sync client deep dive and sync troubleshooting.
• Known Folder Move — IT redirects Desktop, Documents, and Pictures into OneDrive, so the files users actually lose in laptop incidents are the ones automatically protected. This is the closest thing Microsoft 365 has to built-in workstation backup, and it should be policy, not opt-in: Known Folder Move.
• Sharing — any file or folder can be shared by link, internally or externally, governed by tenant and site policies. The link types and their consequences are in sharing and permissions.
• Versioning and recovery — version history on every file, a recycle bin, and Files Restore, which rolls an entire OneDrive back to a point in the last 30 days. That last one is the underused gem: it's the self-service answer to ransomware on a user's synced files.
• Mobile apps with offline access and camera-roll upload.
• Office integration — real-time co-authoring, AutoSave, and "share instead of attach" in Outlook all assume the file lives in OneDrive or SharePoint. A file on C:\ gets none of it.

OneDrive vs SharePoint: the one rule

The practical rule fits in a sentence: personal working files in OneDrive, team files in SharePoint or Teams.

The reasoning is organisational, not technical. Files in OneDrive belong to a person; when that person leaves, their OneDrive enters a countdown to deletion and someone has to rescue what mattered. Files in SharePoint belong to a site with an owning team, and survive any individual's departure. So the smell test: if a OneDrive file has more than a couple of sharing links on it, it has become a team file living in the wrong place — move it. The habit of "important project file shared from someone's OneDrive" is how organisations end up doing archaeology in departed employees' accounts.

Storage boundaries, quota mechanics, and the retention countdown for leavers are covered in storage quotas and limits.

Business vs consumer OneDrive

Two distinct products share the name:

• OneDrive for Business — comes with work/school accounts, lives in your tenant, governed by your policies.
• OneDrive personal — comes with consumer Microsoft accounts and Microsoft 365 Family/Personal.

They are separate services with separate storage, sharing models, and controls, and the sync client will happily sign in to both on the same machine unless you stop it. Most organisations should: allowing personal OneDrive on managed devices is a data-leak path DLP won't fully see. The differences and the blocking mechanism are in OneDrive for Business vs personal.

What admins actually control

OneDrive administration lives in the SharePoint admin center (that platform inheritance again) plus Intune for client rollout:

• Sharing policy — the tenant-wide external sharing dial, default link types, and per-user overrides.
• Sync policy — silent sign-in, Known Folder Move enforcement, blocking unmanaged devices or personal accounts, bandwidth limits. The recommended set is in sync admin best practices.
• Storage defaults and retention — per-user quota and how long a departed user's OneDrive survives (default 30 days, configurable up to ten years).
• Access control — conditional access integration, unmanaged-device restrictions, and session controls for browser access.

For rollouts, the sequence that works: push the sync client and silent configuration first, turn on Known Folder Move once sync is stable, then tighten sharing and device rules — each step invisible to users when done in that order.

Where it fits

OneDrive is the default answer for the personal layer of file storage in Microsoft 365 — and it's at its best when users never think about it: folders sync, versions accumulate, laptops die without data loss, and the interesting collaboration happens one layer up in SharePoint and Teams. If you're moving off file servers, the personal-drive half of that migration is OneDrive's job too — see migrating file shares to OneDrive and SharePoint.