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PowerScale OneFS 7.1.1 and later enable SMB2 clients to access symbolic links in a seamless manner. Many administrators deploy symbolic links to virtually reorder file system hierarchies, especially when crucial files or directories are scattered around an environment.
In an SMB share, a symbolic link (also known as a symlink or a soft link) is a type of file that contains a path to a target file or directory. Symbolic links are transparent to applications running on SMB clients, and they function as typical files and directories. Support for relative and absolute links is enabled by the SMB client. The specific configuration depends on the client type and version.
OneFS exposes symbolic links through the SMB2 protocol, enabling SMB2 clients to resolve the links instead of relying on OneFS to resolve the links on behalf of the clients. To transverse a relative or absolute link, the SMB client must be authenticated to the SMB shares that the link can be followed through. However, if the SMB client does not have permission to access the share, access to the target is denied and Windows will not prompt the user for credentials.
Windows and SMB make a distinction between links to files and links to directories. Once a link is set to be of a certain type, this flag cannot change. Directory links are fully supported in OneFS 8.0 and beyond.
How Windows creates a symbolic link with OneFS
Windows symlinks are created using the SMB protocol by writing a regular file in the initial Create request, then converting it into a symlink with a Set Reparse Point request.
Whenever a PowerScale OneFS node completing an SMB2 request encounters a symbolic link, it returns a Symbolic Link Error Response, which includes the target path (stored in the inode), the remaining section of the original file path, and whether the target path is relative or absolute. From here the client is expected to formulate another request to PowerScale OneFS node, using the details from this response. If there are three symlinks in the path, this process will be repeated three times as each link in the path is reached.
Figure 20 shows an example to create a symbolic file link on Windows client that points to a file on a PowerScale cluster. For detailed steps about how to implement symbolic link with PowerScale, see the Dell article How to create a directory symbolic link in Windows that points to an PowerScale cluster.
Figure 20. Create a symbolic file link that points to a file on a PowerScale cluster
These are some key considerations that we recommend during the design and implementation:
Figure 21. Create symbolic link security policy setting
> dir /AL /S O:\
# cd /usr/likewise/bin
# ./lwregshell
> cd HKEY_THIS_MACHINE\Services\lwio\Parameters\Drivers\onefs
> ls /* to check the current value */
> set_value “SMB2Symlinks” 0 /* 0 to disable, 1 to enable */
Figure 22. Check the current value of SMB2Symlinks on the PowerScale cluster