In the begenning of the article, there is a "Note: Replace volume names with fully-qualified qtree names if working with qtrees"
What does that mean, and what exactly do I need to do?
As I understand, when real DR happened, I need to change the DNS entry, and point source name "system A" to the DR storage, I also need to name all volumes/qtrees/shares on DR filer are the same as those on the primary, so, when I access the primary: systemA:/volume1, after the DR, I'd use the same reference. Those are what I need to do.
It just means if you are using volumes with qtrees, then you would need to ensure the qtree name on the DR side matches the qtree on the primary side as well as the containing volume. So, as long as all the volumes and qtrees are named the same on both primary and DR, then as you say, updating DNS to point to the DR filer would avoid having the clients have to update their details. Most NFS mounts would likely have to be re-mounted anyway to avoid stale handles.