We have recently stacked 3 switches using the provided stacking cables and come to realize that our backups are taking double the time to complete when connected to the stack as opposed to a standalone switch both are in the same subnet and not crossing any firewalls... basically going sideways
I thought stacking was to improve performance not hinder it
we also notice that thestack is one of our top talkers on that subnet
What version is the firmware on the stack? Is there a lot of data being transferred between stack members? It is possible to have more network traffic than the stacking cables can handle.
I would try updating the firmware, Spanning-tree traffic could do it, the stacking ports can only handle so much traffic at once.