Did you already check the hardware, especially the controller cache/battery? If there's an issue with the battery, the controller will switch from write-back to write-trough mode.
As a side not, HP released a couple of urgent advisories for Gen8 servers. One which requires a Microcode upgrade for v2 CPUs, and another one which requires iLO to be upgraded to v1.51 to avoid possible PSOD's. Both fixes are included in the June SPP.
André