Synology iCloud Sync: How It Works & Setup

Synology iCloud sync lets you copy files between your Synology NAS and your iCloud Drive, so you can back up or consolidate cloud data on your own hardware. You set it up with the built-in Cloud Sync app, which connects to iCloud Drive and then mirrors, backs up, or one-way syncs selected folders. This article explains what the tool actually does, what it cannot do, and how to avoid the common pitfalls people hit when using it.

What Synology Cloud Sync Actually Does

Cloud Sync is a free package on Synology DiskStation Manager (DSM) that links a local NAS folder to a cloud storage service. When you add iCloud Drive as a provider, Cloud Sync creates a link between a folder on your NAS and the iCloud Drive folder you authorize. It then transfers files in the direction you choose:

• Bidirectional sync – changes on either side are copied to the other, so both stay identical.
• Download remote changes – files added or changed in iCloud Drive are pulled to the NAS, but nothing is uploaded.
• Upload local changes – files added or changed on the NAS are pushed to iCloud Drive, but remote changes are ignored.

For most people, the useful setup is one-way download: it creates a local backup of iCloud Drive content (documents, desktop folders, photos, etc.) without risking accidental deletion in the cloud. Bidirectional sync is riskier because deleting a file on one side deletes it on the other, and iCloud Drive’s own versioning is limited.

What iCloud Drive Sync Does NOT Cover

The biggest misconception is that Cloud Sync can back up your entire iCloud account, including photos, contacts, calendars, and device backups. It cannot. Cloud Sync only sees iCloud Drive – the file-storage part of iCloud. It does not access:

• iCloud Photos library (unless you enable “Download and Keep Originalsâ€� and sync the Photos folder, which is not a true library backup)
• Contacts, calendars, reminders, notes (these are database-backed, not plain files)
• Device backups (iPhone/iPad backups are stored in iCloud, not in iCloud Drive)
• Mail, Keychain, or Health data

If you want to back up photos, you would need to use Synology Photos’ backup feature or manually copy the files. Cloud Sync is a file-level tool, not an account-level backup.

How to Set Up Synology iCloud Sync

The setup takes about 10 minutes and requires your Apple ID credentials. Here are the steps for current DSM versions:

1. Install Cloud Sync from the Synology Package Center (it is free).
2. Open Cloud Sync and click “+� to create a new sync task.
3. Select iCloud Drive from the provider list. If you don’t see it, update DSM and Cloud Sync to the latest versions.
4. Sign in with your Apple ID. Apple will send a two-factor authentication code to your trusted device – enter it when prompted.
5. Choose the local folder on the NAS (e.g., /volume1/icloud-backup) and the remote folder (usually the root of iCloud Drive, but you can pick a subfolder).
6. Select the sync direction: for a backup, choose “Download remote changes�.
7. Set the schedule (e.g., run every hour) and encryption options if you want the local copy encrypted.
8. Click Apply – Cloud Sync will start the initial transfer.

After the first sync, subsequent runs are incremental, so only changed files are transferred. You can monitor progress in the Cloud Sync main screen or via DSM notifications.

Common Problems and How to Fix Them

Users often run into a few recurring issues:

• Authentication errors – Apple’s two-factor authentication can cause Cloud Sync to fail if the session expires. Re-link the account by editing the task and re-entering credentials.
• “Folder not foundâ€� on iCloud Drive – If you change the remote folder in iCloud, the task breaks. Re-select the remote folder in Cloud Sync.
• Files not downloading – iCloud Drive may keep files “in the cloudâ€� (optimized) rather than physically on the server. Cloud Sync can only download files that are actually stored; if a file is evicted, it may be skipped. In iCloud settings, set “Download and Keep Originalsâ€� to ensure all files are present.
• Sync conflicts – When a file is edited on both sides before sync, Cloud Sync creates a conflict copy (e.g., “filename (conflicted)â€�). This is normal; you must manually merge or choose the correct version.
• Large initial sync – If you have hundreds of GB, the first sync can take days. Use a wired connection and set the schedule to run continuously until it finishes.

How to Choose the Right Sync Direction

The direction you choose depends on your goal:

• Backup of iCloud Drive – Use Download remote changes. This creates a one-way copy on the NAS. If you accidentally delete a file in iCloud, it still exists on the NAS (but note: Cloud Sync may delete it locally if the remote deletion syncs – to avoid that, use the “Backupâ€� mode instead of “Syncâ€� mode, if available).
• Access files from multiple devices – Use Bidirectional sync if you want the NAS to be another client of iCloud Drive. This is not recommended because iCloud Drive is not designed for multi-client sync like Dropbox; it can cause conflicts.
• Migrate data to iCloud – Use Upload local changes to push a local folder to iCloud Drive. This is useful for moving data off the NAS, but be careful: if you delete a file locally, it will be deleted in iCloud.

For most users, the safest is one-way download. If you want a true backup that never deletes local files, check if Cloud Sync has a “Backup� mode (some providers do; iCloud Drive may only offer sync modes). In that case, consider using Hyper Backup to a local shared folder instead, which keeps versions.

Costs and Limitations

Cloud Sync itself is free, but you need a Synology NAS (hardware cost) and enough storage on the NAS for the iCloud Drive content. iCloud Drive storage is billed by Apple; the free tier is 5 GB, and paid plans go up to 2 TB or more. Cloud Sync does not add any extra cost, but it does consume bandwidth and NAS resources. The main limitation is that iCloud Drive is not designed for third-party sync; Apple may throttle or require periodic re-authentication. Also, Cloud Sync does not support iCloud Photos, as mentioned, so you cannot use it to back up your photo library directly.

Alternatives to Synology iCloud Sync

If Cloud Sync does not meet your needs, consider these options:

• rclone – A command-line tool that can mount iCloud Drive as a network drive or sync it. It gives more control but is harder to set up.
• Synology Drive – If you want to sync files between your computer and NAS, this is a better tool, but it does not connect to iCloud.
• Manual download – Download files from iCloud.com to your computer and then copy them to the NAS. Simple but not automated.
• Apple’s iCloud for Windows – If you have a PC, you can sync iCloud Drive to the PC and then use Synology Drive to sync that folder to the NAS. This gives a two-hop sync but works.

Frequently Asked Questions

Can I sync iCloud Photos with Synology? No, Cloud Sync only works with iCloud Drive, not the Photos library. Use Synology Photos’ backup feature on your phone to back up photos directly.

Will Cloud Sync delete files on my NAS if I delete them in iCloud? In bidirectional sync, yes – deletion is mirrored. In one-way download mode, it depends on the task settings; some versions delete local files when remote files are removed. To avoid this, use a backup tool like Hyper Backup instead.

Why does Cloud Sync keep asking me to sign in to Apple? Apple invalidates tokens periodically, especially with two-factor authentication. Re-link the account and consider using an App-Specific Password if you have two-factor enabled (available in your Apple ID security settings).

Does Cloud Sync work with iCloud Drive on Windows? Cloud Sync runs on the Synology NAS, not on your computer. It connects directly to iCloud Drive over the internet, so it works independently of your computer’s OS.

Can I schedule sync to run only at night? Yes, in Cloud Sync you can set a schedule to run the task at specific times or intervals. This helps reduce bandwidth usage during the day.

Is my data encrypted on the NAS? Cloud Sync offers an encryption option for the local copy. If you enable it, files are stored encrypted on the NAS, and you need a passphrase to restore them. This is useful for sensitive data.

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