How to Configure Time Machine Backup over SMB Network Shares on macOS

Introduction

Time Machine is Apple’s built-in backup feature for macOS, designed to automatically back up all your files, including apps, music, photos, email, and documents. While many users connect a physical external hard drive for Time Machine, configuring it to back up over the network to a Server Message Block (SMB) share is far more convenient for laptops and distributed environments. This guide explains how to set up an SMB network share as a Time Machine destination.

Requirements

Before configuring macOS, ensure your network attached storage (NAS) or Windows Server meets the following requirements:

• The file share must use the SMB protocol.
• The server must support the Time Machine over SMB specification, which requires support for the F_FULLFSYNC extension and Bonjour discovery (though Bonjour is not strictly required if connecting manually).
• A dedicated user account with read/write permissions to the share.

Step 1: Connect to the SMB Share

First, you must establish a connection to the network share from your Mac.

1. Open Finder.
2. In the menu bar, click Go > Connect to Server (or press Command + K).
3. Enter the address of the share using the SMB prefix. For example: smb://192.168.1.100/TimeMachineBackup.
4. Click Connect.
5. When prompted, enter the username and password for the dedicated backup account. Check the box to Remember this password in my keychain so Time Machine can connect automatically in the background.

Step 2: Select the Disk in Time Machine

Once the network share is mounted, you can configure Time Machine to use it.

1. Open System Settings (or System Preferences on older macOS versions).
2. Navigate to General > Time Machine.
3. Click Add Backup Disk… or click the + button.
4. A list of available disks will appear. Your newly mounted SMB share should be listed. Select it and click Set Up Disk.
5. You may be prompted to enter the network credentials again. Ensure you do so to grant Time Machine permanent access.

Step 3: Encrypt the Backup (Highly Recommended)

During the setup process, macOS will ask if you want to encrypt the backup disk. It is highly recommended to toggle Encrypt Backup to on. Because the backup resides on a network share that could potentially be accessed by administrators or attackers, encrypting the sparse bundle (the file that holds the backup) ensures your data remains secure. Enter a strong password and store it safely; if you lose this password, your backups will be unrecoverable.

Step 4: Manage Storage Quotas

Time Machine is designed to consume all available space on the destination drive before deleting the oldest backups. If your SMB share is on a large volume, Time Machine might consume terabytes of data. To prevent this, you should set a storage quota.

Most modern NAS systems (like Synology or QNAP) allow you to set a user-level or folder-level quota directly in their admin interfaces. Set the quota to 2 or 3 times the size of the Mac’s internal drive. For example, if backing up a 512GB Mac, set the SMB user quota to 1.5TB. Time Machine will respect this limit and begin pruning old backups when it hits the quota.

Conclusion

Once configured, Time Machine will perform hourly backups whenever the Mac is connected to the same network as the SMB share. Because the initial backup transfers the entire contents of the disk over the network, it can take several hours or even days. Ensure your Mac remains powered on and connected to power during the first sync.