adaptively varying a destage rate of said NVS according to a current storage occupancy of said NVS;

maintaining said high threshold level for said NVS;

maintaining a low threshold level that is set to be a predetermined fixed amount below said high threshold level;

setting said destage rate of said NVS to be zero when the NVS occupancy is below said low threshold level;

setting said destage rate of said NVS to be maximum when said NVS occupancy is above said high threshold level;

linearly increasing said destage rate of said NVS from zero to maximum as said NVS occupancy goes from said low threshold level to said high threshold level;

maintaining a desired occupancy level for said NVS;

maintaining a max occupancy observed variable for said NVS;

initializing said high threshold level to be equal to a desired occupancy level, wherein said high threshold level is constrained to never exceed said desired occupancy level;

if said NVS occupancy drops below a current high threshold level, and if said max occupancy observed variable is greater than said desired occupancy level, decrementing and backing-off said high threshold level by a positive difference between said max occupancy observed variable and said desired occupancy level; and

resetting said max occupancy observed variable.