computurd

you may be right about the disk cache policy, it is however a bit more to it.

DIO = for reads all data is bypassing the controllers cache, except when read ahead is enabled, for writes all data bypasses the controllers cache except when WB is enabled
CIO = all data passes through the controllers cache including writes even when WT is enabled.

BTW, CIO is being deprecated.

Given this, one can do iometer read tests on the LSI using 1GB filesize as long as DIO is enabled, for writes WT must be enabled.

Link to LSI document

As for the disk cache policy, the setting does make an impact in some benchmarks (depends on the SSD), I haven't spent much time testing it though.