OneDrive vs Google Drive on Windows: Two Sync Engines, Two Very Different Disk Habits

Two engines with opposite philosophies

OneDrive's Files On-Demand keeps a lightweight placeholder for every file. Opening it hydrates the full file at its real path, “Free up space” returns it online-only, and “Always keep on this device” pins a full copy. Under Storage Sense pressure, OneDrive will even dehydrate files you have not opened for a while — the local footprint stays honest.

Google Drive for desktop takes the opposite route: it mounts a virtual drive letter where nothing exists locally until you read it. Files then stream through a content cache as you open them. The optional Mirror mode flips the philosophy entirely — a complete second copy of your library lives in the user profile, on top of whatever the cache holds.

Where the gigabytes actually go

Neither client shows its full footprint in one place, so people guess — and guess wrong. The breakdown below covers every place these two engines put real bytes on an SSD. Check both folders in Explorer once a month and the surprises disappear.

• An online-only OneDrive placeholder costs kilobytes of metadata, not the file itself
• Pinned OneDrive files are full local copies that stay until you free them up
• Streamed Drive files pass through the content cache at %LOCALAPPDATA%\Google\DriveFS
• Mirror mode keeps a complete second copy of My Drive inside your user profile
• A stuck OneDrive sync is fixed by onedrive.exe /reset — which rebuilds local state and restarts every download
• Both clients keep logs — small, but the first thing support asks for

Which one leaves your SSD alone

For huge libraries you rarely open, Drive's streaming is lighter. Nothing hydrates permanently, and the cache can be capped or cleared in the app's settings. For documents you work in daily, OneDrive pinning is more predictable — you always know which folders are fully local, and version history keeps working offline.

The practical setup is a hybrid. Pin the active project, free up space before a big migration, and cap the DriveFS cache on small SSDs before Windows starts complaining. The engine matters less than knowing which mode each folder is in — that single habit prevents both “disk full” surprises and accidental offline gaps.

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