The Product Announcements Guide for DP 8 shows this:
The
Backup POSIX hard links as files (-hlink) option is not available on OpenVMS.
Files with multiple directory entries are only backed up once using the primary path name.
The secondary path entries are saved as soft links. During a restore, these extra path entries
will also be restored.
In the GUI, if you click on 'Help -> Help Topics' and search for POSIX Hard Links, for UNIX file systems, it says:
If there are multiple hardlinks referencing the same file, the file is backed up only once. You can change this by setting the Backup POSIX hard links as files option.
UNIX filesystem specific option.
This option directs how Data Protector backs up hard links.
The default is OFF. When you back up hard links as links, Data Protector traverses the directory trees twice. This allows Data Protector to estimate the size of the backup, however, this takes extra time. Only one hard link is backed up with the file contents, while all the others are backed up as hard links.
If set to ON, Data Protector will back up the entire file contents for each hard link. Data Protector traverses the filesystem tree only once, thus significantly speeding up the backup process. Use this option when there are no hard links in your directory. When this option is set to ON, Data Protector cannot estimate the size of the backup or display the percentage of the backup finished.
We basically use this as a method of turning off one of the UNIX treewalks to improve backup performance
This capability has been around forever, so I don't know if this really answers your question