Storm season is back, bringing with it the potential for significant weather events. If you have clients in areas prone to infrastructure disruption, visit the Disaster Recovery Resources guide for preparedness information. Datto recommends performing proactive disaster recovery testing to mitigate potential downtime. See our articles about the importance of disaster recovery testing and Preparing For A Cloud Virtualization Test: Policies, Procedures, And Partner Responsibilities to learn more. For live updates, follow @datto on Twitter.

Backing up an External Share with NAS Guard



This article explains how to use the NAS Guard feature available on Datto SIRIS, Datto ALTO, and Datto NAS.


  • Datto SIRIS
  • Datto ALTO
  • Datto NAS


The NAS Guard feature allows you to back up an SMB share from any system to your Datto appliance. The snapshots it takes are stored locally, and then can then be replicated to the Datto Cloud by your Datto device.


NAS Guard does not natively support external share names which contain spaces. Datto recommends renaming these shares if possible. If you need to protect a share with spaces in its name, contact Datto Technical Support for assistance.


1. Access the Datto appliance GUI. Navigate to File Share  → Network Attached Storage.

2. Click Backup External Share.

Figure 1: Backup External Share (click to enlarge)

3. You will see the Select System prompt. Enter a name for the share in the Share Name field.

4. Fill in the SMB Address. This value should be the fully-qualified path of the share as it exists in the production environment.

5. From the Retain NTFS File Permissions dropdown, select Yes or No.

  • If you select Yes, the files and folders in the NAS share will be backed up with their full ACLs intact. Choosing this option may increase backup times.

6. Fill in the Credentials field if necessary. Datto strongly recommends using the credentials of a system administrator who has full access to all of the content in the share. Using a restricted account can prevent your Datto appliance from being able to read and perform a complete backup of the share's file structure.

If no credentials are needed to connect to and access the share, you can check the Connect as a Guest box.

7. Click Next.

Figure 2: Select System (click to enlarge)

6. Create a Local Snapshot & Retention schedule for the share. Then, click Next.

Figure 3: Set Local Snapshot & Retention (click to enlarge)

7. Create a Cloud Snapshot & Retention schedule for the share. Then, click Next.

Figure 4: Set Cloud Snapshot & Retention (click to enlarge)

8. Review the summary, and then click Finish.

Figure 5: Review & Confirm (click to enlarge)

9. Your share will now back up to the Datto appliance according to the schedule you set.

Figure 6: Protected NAS share (click to enlarge)


Q: Is there a limitation to share size?
A: The current share size limit is 16 TB. If the NAS device or share you will be protecting is smaller than that, or lacks the free space, the working share size will also be lower. The share on the Datto appliance cannot be resized after you create it.

Q: If my share is on a domain, should I join the Datto appliance the domain?
A: Yes, you will need to join the Datto device to the domain as well. This will allow the Datto appliance to connect to the external share using domain credentials.

Q: Are the share name and username I enter case-sensitive?
A: It is a best-practice to respect case for the share name and username. Although certain systems will disregard case, others may not.

Q: Does NAS Guard preserve Unix permissions?
A: Depending on your environment, NAS Guard may or may not be able to preserve Unix permissions. Datto strongly recommends testing a restore to verify whether your users' permissions can be restored. 

Q: How would I add a group as read-only for a share?
A: Permissions within the share will reflect the permissions on the external share. There should be no need to add the same permissions to the share on the Datto appliance.

Q: Which Datto appliances are able to use this feature?
A: Currently any device running Datto IRIS 3, excluding Alto 1.

Q: Do I need to install anything on my hardware to back up my share?
A: You do not need to install any software. The Datto appliance will not make any modifications to the share during the pairing or backup processes. All external shares mount on the Datto appliance as read-only.

Q: What are my restore options?
You have the capability to mount file restores with or without NTFS permissions of snapshots from the Restore tab of the Datto appliance. You can also mount file restores from the Recovery Launchpad.

Q: Is there a limit to the number of shares I can have on the Datto appliance?
A: There is currently no limit, although the collective size of the shares would determine how many you could add.

Q: Is there a way I can put a limit on share sizes?
A: The limit for the share's size is determined by the Datto appliance on pairing. Any limit on the overall usage of the share would depend on how much change happens in the backups, and the retention settings to limit the overall growth.

Additional Resources

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