When this feature is disabled or unavailable, each symlink is traversed and the data it links to is backed up. Because of this, unnecessary data can sometimes be backed up and in certain situations the application might end up in a loop. Backing up the symlinks instead avoids these issues. And because the symlink files are very small compared to the data in most cases, the backups take less time to complete. The overall performance of the cluster can also improve because of the reduced IO operations.

This feature is supported for backup applications running on Windows. You should understand the relevant technical aspects of the environment before using it.

Windows supports extended attributes (EA) which collectively form additional metadata optionally associated with the files. These attributes are used by various applications, such as the Windows Subsystem for Linux as described at File Permissions for WSL. Applications can request extended attributes for each file when reading data from ONTAP.

The symlinks are returned in the extended attributes when the feature is enabled. Therefore a backup application must provide standard EA support which is used to store the metadata. Some Windows utilities support and preserve the extended attributes. However, if the backup software does not support backing up and restoring the extended attributes, it will not preserve the metadata associated with each file and fail to process the symlinks properly.

Backup applications running on a Microsoft Windows server can be granted a special privilege allowing them to bypass normal file security. This is typically done by adding the applications to the Backup Operators group. The apps can then back up and restore files as needed as well as perform other related system operations. There are subtle changes to the SMB protocol used by the backup applications which can be detected by ONTAP as the data is read and written.

The symlink backup feature has several requirements including: