Negative write caching rate

I have been researching write caching rates in an attempt to explain why a number of the sites that I oversee are seeing low write caching rates. In the process I did discover that their level of OLTP write activity is small which means that the basic system administration functions adversely affect the caching rate. But in the process I discovered that there are periods of time when the write caching rate becomes negative. I have seen write caching rates as high as -300% when measured over 1 hour. Further analysis has revealed that this occurs every time that a non-fuzzy (sync) checkpoint is performed during a period of very low levels of activity. The non-fuzzy checkpoint flushes a significant number of pages compared with the the non-checkpoint activity levels My questions are:- How can I tell when these non-fuzzy checkpoints have been performed? Can I determine through a sysmaster query how many pages have not been flushed? regards Mighty M