There are no counters that will show this.  SymmMerge will give you an estimate.  You can usually use a 30-50% estimate for overwrites and be in the ballpark.
Hi  I was looking at the presentation from EMC World 2014 and the FA workloads. Can anyone advise what metrics in STP we would look at for overwrites/writes to new slots? We can get the basic amount on writes for the FA %write, write reqs per sec but is there a way to separate these out?  Thanks Al
overwrites and writes to new slot monitoring.