Dropbox vs Google Drive vs OneDrive vs iCloud: Cloud Sync Local Storage Comparison for Mac (2026)

If your Mac's storage warning keeps firing even though you use cloud sync, you are not imagining things. A cloud sync local storage comparison on macOS reveals surprising differences between Dropbox, Google Drive, OneDrive, and iCloud Drive — in default download behavior, cache ceilings, and how well each service actually offloads data. This guide covers what each service stores locally by default, where to find it, and how to measure it accurately.

Why Cloud Sync Still Uses Local Disk Space

Every major sync service keeps some files local, either because you asked for offline access, because the app aggressively pre-fetches content, or because it maintains caches and metadata databases separate from the files themselves. The four leading services handle this very differently.

iCloud Drive

iCloud Drive has the tightest integration with macOS because Apple controls both sides of the stack. When "Optimize Mac Storage" is on (System Settings → Apple ID → iCloud → iCloud Drive → Options), macOS can evict files to iCloud and keep only a lightweight stub on disk. This is the most effective online-only model of the four services.

• Default behavior: Files that have not been opened recently are evicted automatically when disk pressure rises. New files sync to iCloud and may stay local until pressure appears.
• Cache and metadata location: ~/Library/Application Support/CloudDocs/ and ~/Library/Mobile Documents/ (the latter is your actual iCloud Drive folder).
• Daemon caches: ~/Library/Caches/com.apple.bird/ — the bird daemon manages iCloud eviction and re-download.

The iCloud approach is the most storage-efficient on a Mac with limited SSD because macOS itself coordinates eviction. The trade-off: you must be online or patient when opening an evicted file.

Dropbox

Dropbox's macOS client defaults to online-only (Smart Sync) on most accounts, meaning files appear in Finder but are not physically on disk until you open them. However, any file you open is then downloaded and kept locally until you explicitly make it "online only" again.

• Default behavior: Smart Sync is on by default for Business accounts; Personal accounts may default to local mirroring depending on account history and client version. Check Preferences → Sync → Default new files.
• Local folder: ~/Dropbox/ (or wherever you placed it during setup).
• Cache: ~/.dropbox/ contains the sync database and metadata; a separate disk cache lives at ~/.dropbox/instance1/. Dropbox does not publish a hard cap on this cache, and it can grow to several gigabytes on large accounts.
• LevelDB databases: Dropbox stores file metadata in LevelDB format under ~/.dropbox/. Do not delete these manually — Dropbox will regenerate them, but the process can take hours.

The practical risk with Dropbox is "quiet accumulation": you open files to read them, they stay local, and over time your local Dropbox folder mirrors more than you intended.

Google Drive (for Desktop)

Google Drive for Desktop replaced the older Backup and Sync and Drive File Stream clients. It operates in two modes: Stream files (online-only by default, files download on demand) and Mirror files (full local copy). Most fresh installs default to Stream.

• Default behavior: Stream mode — files live in a virtual FUSE filesystem mounted at /Volumes/Google Drive/. Only files you pin or open are written to the local cache.
• Cache location: ~/Library/Application Support/Google/DriveFS/. This directory contains the content cache, chunk database, and metadata. There is no user-configurable cap exposed in the UI; Google Drive manages cache size internally based on available disk.
• Log files: ~/Library/Logs/Google Drive/ — safe to inspect but do not delete while the client is running.
• Mirror mode warning: If you switched to Mirror files, your entire Google Drive is downloaded to ~/Google Drive/My Drive/. For large Workspace accounts this can be tens or hundreds of gigabytes.

Google Drive's FUSE approach means the virtual volume does not count against your visible disk usage in the same way a real folder does, which can make it harder to audit with a standard disk map. Files in the content cache, however, consume real space.

Microsoft OneDrive

OneDrive on macOS supports Files On-Demand, which is equivalent to Smart Sync and iCloud's online-only mode. When enabled, files show a cloud icon and are not present on disk.

• Default behavior: Files On-Demand is on by default. Personal (Microsoft account) and work/school (Microsoft 365) accounts both support it on macOS 12+.
• Local folder: ~/Library/CloudStorage/OneDrive-Personal/ or ~/Library/CloudStorage/OneDrive-[OrgName]/ — Apple's CloudStorage framework is used since macOS Monterey, which is the same mount point format used by iCloud.
• Cache and metadata: ~/Library/Application Support/OneDrive/ and ~/Library/Caches/com.microsoft.OneDrive-mac/.
• Known issue: OneDrive can leave behind orphaned .849C9593-D756-4E56-8D6E-42412F2A707B temporary files when uploads are interrupted. These are safe to delete after confirming OneDrive is not actively syncing.

Cloud Sync Local Storage Comparison: Summary Table

How to Measure Each Service's Real Disk Footprint

The Finder "Get Info" panel can undercount online-only files. For accurate numbers, use Terminal.

Check iCloud Drive local usage

du -sh ~/Library/Mobile\ Documents/ 2>/dev/null

Check Dropbox local usage

du -sh ~/Dropbox/ ~/.dropbox/ 2>/dev/null

Check Google Drive cache

du -sh ~/Library/Application\ Support/Google/DriveFS/ 2>/dev/null

Check OneDrive local usage

du -sh ~/Library/CloudStorage/OneDrive-*/ ~/Library/Caches/com.microsoft.OneDrive-mac/ 2>/dev/null

Run these commands with Dropbox, Google Drive, and OneDrive all running normally so the numbers reflect what the clients are actually maintaining.

Auditing All Four at Once with Crumb

If you would rather see all four services side by side in a visual disk map, Crumb's Visualize tab scans your entire Mac — including ~/Library/CloudStorage/, ~/Library/Application Support/Google/DriveFS/, ~/.dropbox/, and ~/Library/Mobile Documents/ — and surfaces their real sizes in a single interactive treemap. Because Crumb runs natively and locally, it reads the actual bytes on disk rather than the logical sizes each service reports. This makes it straightforward to compare the real local footprints without running four separate Terminal commands and mentally adding them up.

Crumb's "Is this safe to delete?" AI can also explain any unfamiliar subfolder you encounter inside a sync cache before you remove it — useful when you find something like Google Drive's per-account/ chunk directories and want to know whether clearing them mid-sync is safe (it usually is not while the client is running). You can download Crumb and run a one-time scan for free.

What Is Actually Safe to Delete

A few ground rules before clearing anything:

• Never delete sync databases while the client is running. Dropbox's ~/.dropbox/ LevelDB files, Google Drive's DriveFS/ chunk cache, and OneDrive's metadata stores will cause re-indexing or data loss if removed live.
• Log files are generally safe. Contents of ~/Library/Logs/Google Drive/ and similar log directories can be cleared when the client is quit. Reclaim is usually modest (tens of MB).
• Evicting files is different from deleting them. Making a file "online only" in any of these services removes the local copy but keeps it in the cloud. Deleting the file removes it from both. These are not the same action.
• iCloud's bird cache: Do not manually delete ~/Library/Caches/com.apple.bird/. macOS manages this and clearing it can cause sync stalls. Use "Optimize Mac Storage" instead and let the OS reclaim space naturally.

Which Service Uses the Least Local Space by Default?

On a fresh install with default settings, iCloud Drive is the most aggressive at reclaiming local space because macOS coordinates eviction at the OS level. Google Drive in Stream mode is a close second — the FUSE mount is lightweight and the content cache grows only as you open files. OneDrive with Files On-Demand behaves similarly. Dropbox Personal accounts have historically defaulted to full local mirroring on legacy installs; if you have been using Dropbox for years, check your Sync preferences — you may still be mirroring everything locally.

The honest answer is that no single service is universally "best" for storage efficiency. The differences come down to your usage pattern: how many files you open regularly, whether you have offline access enabled, and whether you or your IT administrator have changed the defaults. Auditing the real numbers periodically — rather than guessing — is the only reliable way to know what each service is actually consuming on your Mac.