iCloud Sync Slow on Mac? Here's What's Going On

You drop a 200 MB file into iCloud Drive on your Mac, and three hours later your iPhone still hasn’t seen it. Or your Photos library claims it’s “Updating Library” and the count of remaining items hasn’t moved in two days. Or Notes that you typed an hour ago haven’t reached your iPad.

iCloud sync slowness can mean many different things, and Apple’s status indicators are notoriously vague. Here’s how to figure out what’s actually happening on macOS Sonoma 14 and Sequoia 15, and what you can do about each cause.

Step 1: Find out if it’s actually syncing

The first question is whether sync is running at all. Apple gives you one user-facing status: a tiny cloud icon in Finder for iCloud Drive folders. That’s not enough.

Open Activity Monitor → Network tab. Sort by “Sent Bytes” descending. Look for these processes:

• bird: the iCloud Drive sync daemon.
• cloudd: general cloud sync (CloudKit).
• photolibraryd: Photos library sync.
• NotesMigrator / Notes: Notes sync (when active).
• Mail: when syncing IMAP/iCloud mail.

If bird is sending 50 MB/s, sync is just slow because of bandwidth — wait. If it’s sending 0 KB/s while you have GBs queued, sync is stuck.

You can also run from Terminal:

brctl status

This dumps detailed iCloud Drive sync state for every container. Look for “items pending upload” and “items pending download.” If those numbers are nonzero but unchanged after 30 minutes, sync is hung.

Step 2: Check iCloud system status

Apple’s iCloud servers occasionally have outages. Visit Apple’s System Status page (https://www.apple.com/support/systemstatus/). If “iCloud Drive” or “iCloud Photos” shows yellow or red, the issue is on Apple’s side — wait it out.

This sounds dismissive, but Apple has shipped sync regressions in major macOS releases that took weeks to fix. If the issue started right after an OS update, check for an Apple support thread before doing anything destructive.

Step 3: Check the bandwidth

Run a speed test (fast.com). If your upload is 5 Mbps, uploading 100 GB of Photos to iCloud will take roughly 50 hours of solid uploading — that’s not “stuck,” that’s just upload-limited.

Common bandwidth-eaters that compete with iCloud:

• Time Machine to a NAS.
• Backblaze / Carbonite / Arq backups.
• Dropbox / OneDrive / Google Drive sync running in parallel.
• Game launchers downloading updates.
• Steam / Epic auto-updates.

Quit or pause everything except iCloud, then re-test sync speed.

Step 4: Check if iCloud is throttled

Apple deliberately throttles iCloud sync when:

• The Mac is on battery (sync slows to a trickle).
• Low Power Mode is on.
• Network is metered (System Settings → Wi-Fi → Details → “Low data mode” enabled).

Plug in, disable Low Power Mode, disable Low Data Mode, and watch sync resume.

Step 5: Restart the sync daemons

If sync is stuck at zero bytes per second, the daemons are usually hung. Open Terminal:

sudo killall bird
sudo killall cloudd
killall photolibraryd

(bird and cloudd need sudo because they restart at the system level; photolibraryd is per-user.)

launchd will restart all three. Watch Activity Monitor for them to come back, then check if sync started moving.

Step 6: Sign out and back into iCloud

If killing the daemons doesn’t help, the auth tokens are usually stale. System Settings → Apple ID → Sign Out (choose to keep local copies of your data). Sign back in.

This forces a full re-handshake with iCloud servers and reissues all sync tokens. It can take a long time afterward as the Mac re-indexes everything, but the underlying bottleneck usually clears.

Skip the manual huntSweep finds the cached configs, leftover daemons, and stale prefs across your Mac. Download Sweep free →

Step 7: Check disk space

iCloud Drive needs free local disk space to download. If your Mac has 500 MB free and you’re trying to download 50 GB of photos, sync will appear paused indefinitely.

Apple menu → About This Mac → More Info → Storage → click Storage Settings. If your Mac is over 90% full, that’s your sync bottleneck.

Free up at least 20% of disk space before expecting sync to resume normally. This is also where Sweep helps with non-iCloud cleanup: it surfaces caches, log files, leftover app data, and large files you’ve forgotten about, often freeing 10-50 GB on a typical Mac.

There’s a faster waySweep does the cleanup in seconds — caches, logs, leftover app data, and large stale files. Try Sweep free →

Step 8: Photos library specifics

iCloud Photos has its own peculiarities:

• “Updating Library” can sit on the same number for hours while it processes metadata; it’s not actually stuck.
• Original-quality download takes much longer than thumbnails — the library shows full size but the originals trickle in.
• A library with hundreds of thousands of photos can take days to fully sync after sign-in.

Check progress: open Photos → Library tab → scroll to the very bottom. Apple shows the sync status there (“X items uploading,” “Updating,” etc.).

If Photos says “Pause Sync” at the bottom, click it to resume. Sync occasionally pauses itself when battery is low or network is poor.

Step 9: iCloud Drive specifics

The “bird” daemon manages iCloud Drive. Its scratch space lives in:

~/Library/Application Support/CloudDocs/

If something corrupts there, sync fails. The cleanest fix:

1. Sign out of iCloud (keep local copies).
2. Quit all apps.
3. Move ~/Library/Application Support/CloudDocs/ to the desktop.
4. Sign back into iCloud.

The folder rebuilds. Sync resumes from scratch (which can be slow but reliable).

Step 10: Check if it’s just one file

Sometimes one specific file is the bottleneck. iCloud Drive will get hung trying to sync a 50 GB video file or a file with a name iCloud’s server doesn’t accept.

Look for the iCloud cloud icon next to files in Finder:

• Solid filled cloud = waiting to download.
• Dashed cloud = uploading.
• No icon = local and synced.

If a specific file has been “uploading” for hours, move it out of iCloud Drive temporarily, let other items sync, then move it back. Or compress it first (a single .zip uploads more reliably than a folder of 5,000 small files).

Step 11: Check for naming or content issues

iCloud Drive rejects:

• File names with certain special characters.
• File names over 255 bytes (Unicode characters count as 2-4 bytes each).
• Files larger than 50 GB.
• Files in .app bundles inside iCloud Drive (sometimes).

If sync stalls on a particular folder, the contents likely include a file iCloud can’t accept.

Step 12: Check the network for VPN / proxy issues

A VPN that routes traffic through a slow exit node will make iCloud sync slow. Disconnect the VPN and re-test.

Even after disconnection, an old VPN’s network extension may still intercept traffic.

systemextensionsctl list

Remove any extensions from VPNs you no longer use.

Step 13: DNS issues

iCloud connects to many Apple-owned hostnames. If your DNS is slow or filtering, iCloud connections take longer to establish.

Test:

dig @1.1.1.1 p10-content.icloud.com
dig @8.8.8.8 p10-content.icloud.com

Compare resolution times. If your current DNS is much slower, switch:

System Settings → Network → Wi-Fi → Details → DNS → add 1.1.1.1 and 8.8.8.8.

Step 14: When iCloud just is what it is

Some realities about iCloud sync:

• Photos library upload averages 30-50 GB per day on a fast connection.
• Notes with attachments can take hours to propagate.
• Mail is often slower than IMAP for the same volume.
• iCloud Drive on a 25 Mbps upload connection will never feel “fast.”

If you’ve checked everything and iCloud is just slow because you have a lot of data and a normal home internet plan, that’s not fixable. The first sync after major library imports is always the worst.

What to do when nothing works

If sync stays stuck for more than 48 hours:

• Sign out of iCloud entirely. Restart. Sign back in.
• Try on a different network (a phone hotspot rules out home network issues).
• Make sure iCloud quota isn’t full (System Settings → Apple ID → iCloud → Manage).

The vast majority of iCloud sync slowness is bandwidth, throttling on battery, or a daemon hang that killall bird resolves. Steps 1-5 are where 80% of cases get fixed. Beyond that, give it 24 hours; iCloud often catches up overnight when the Mac is plugged in and the network is quiet.