Hello Greg, I’m running iRST version 12.9 on my system and I was able to see the accelerate option.
It is locate under the performance TAB. Check the image below
If you are still having this behavior with your version, please try the one we have available at downloadcenter.intel.com
Greg, sometimes when the RAID was previously accelerated, the feature will not appear under performance Tab.
In order to disable it, you would have to reinstall the previous RST version 11.7 and disable it from there. You would also need to set the SSD that you are going to use for cache as unallocated under the RAID Bios.
Then, format the SSD and reinstall RST Version 188.8.131.521.
You can try with the version I sent to you on my previous post.