explanations required for sp_sysmon output "pool < prefetch size"

Hi team,

Could anyone explain me the meaning of the sp_sysmon output?

      Large I/Os Denied due to

        Pool < Prefetch Size        337.2         397.2       75861      16.9 %

First I though my 32K buffer pool was too small so I increased it from 9Gb to 12Gb but the value doesn't change at all.

Maybe I should first understand the information before modifying anything.

Thanks

Simon