High Prioritized Demotion

In order to be certain that there is always some room for active flash to do Prompt Promotion of pages to Tier 1, High Prioritized Demotion is used to demote pages out of Tier 1. Pages that have the lowest IOPH are candidates for High Prioritized Demotion. Similar to Prompt Promotion, High Prioritized Demotion does not wait for the current HDT cycle to end to make relocation decisions.

High Prioritized Demotion is only triggered when:

Peak performance utilization is predefined for a particular media.

Performance utilization of a tier is the maximum amount of I/O it can receive. The maximum I/O load that should be targeted to a tier depends upon the media type used to make the tier. A performance utilization of 100% means that the tier is receiving the maximum amount of I/O it can sustain. When performance utilization reaches about the 60% level, response time to the particular media becomes noticeably slower. See Tier relocation workflow for more information on performance utilization.