3 Replies Latest reply: Dec 28, 2014 11:12 AM by Nick Dyer RSS

    missing cache hits

    Tony Wong Adventurer

      i am doing 9 concurrent svmotion to a nimble volume from a emc cx and notive that cache hits a getting missed and going as low as 80%. any idea whats going on? Capture.JPG

        • Re: missing cache hits
          Nick Dyer Navigator

          Hello Tony,

           

          When you perform sequential writes to a Nimble system (in this instance, a Storage vMotion) we automatically bypass writing data into cache, as we cannot have a good idea as to whether the data is hot or not. Therefore what the array does is after the data is on the system the array figures out what data is needed for cache and will pre-fetch copy blocks as and when required.

           

          This is why you're seeing lower cache hits as the data migrated to Nimble is cold, however what you should notice is this warm back up within a few minutes or so.

          • Re: missing cache hits
            Dmitry Marevutsky Newbie

            Hi,

             

            this could be solve with performance policy tuning :

             

            Enable

            perfpolicy --edit name --cache_policy aggressive

             

            Disable

            perfpolicy --edit name --cache_policy normal

             

            please refer in documentation before ( nice document of BP Nimble + vmware)

             

            thanks

             

            Dima

              • Re: missing cache hits
                Nick Dyer Navigator

                Dmitry Marevutsky wrote:

                 

                Hi,

                 

                this could be solve with performance policy tuning :

                 

                Enable

                perfpolicy --edit name --cache_policy aggressive

                 

                Disable

                perfpolicy --edit name --cache_policy normal

                 

                please refer in documentation before ( nice document of BP Nimble + vmware)

                 

                thanks

                 

                Dima

                I'd be very careful enabling Aggressive Caching on any array - in fact it should only be done under the guidance and/or instruction of Nimble Storage Support or Systems Engineers for specific workloads or requirements.

                 

                It's hidden in the CLI for a reason; it's not a tool for everyday use and has the power to be detrimental to your storage array caching if not used wisely.

                 

                In this case (standard Storage vMotions) Aggressive Caching should NOT be enabled.