Hello,
i would suggest releasing the ssd from the RAID system and try the ssd as one with the speed test to see if the issue has to do with the ssd itself. for the firmware update you have to see which modell ssd are you using and see online on the sandisk website if there is a update available to install.
if you see that the ssd without the raid system is again too slow then you are sure what the issue is. but if not then you will have to test all the other parameters as well, like the RAID controller and the other SSD that is in the raid.
