SRDF/A & Read Performance on Symmetrix with Sybase

We have a SRDF/A setup on a DMX-3 and its for a Sybase reporting server installed on a Solaris Box. Reports are performing very slow while

SRDF/A is in use and they are performing quite well while the particular SRDF/A group is suspended. I could think this can be an issue with insufficient cache. But is there any other relation wrt performance difference?