Hi [NAME]  for systems that have NVMe drives, Intel says the BIOS RAID setting is enabled so that the M.2 NVMe drives can have RAID configuration at some time in the future. SATA drives can also be used because BIOS RAID setting also includes AHCI, for systems that have NVMe slots and SATA bay. The old Alienware 15 R3 Storage can have NVMe and SATA drives, and BIOS RAID setting is enabled.  The new Alienware m15 R4 Internal slots are all M.2 PCIe NVMe, and BIOS RAID setting is enabled.  The new Alienware m15 R4 should not have BIOS SATA/AHCI setting enabled. 
Hi all, I recently replaced my dead Alienware 15 R3 with a new M15 R4 laptop. The laptop came with a 1TB m.2 drive that was set to RAID mode in the BIOS. I'm not sure why Dell ships a single drive configuration set to RAID in the BIOS, but maybe there's a reason for this I'm not aware of.I added a 2nd 1TB m.2 drive that Windows assigned D as the drive letter, but I have an external HD that I need to be D, so I tried to change the drive letter in Windows Disk Management. The process hung forever so I had to reboot. I tried once again to change the drive letter using AOMEI Partition Assistant, and again the process hung. While in this app, I noticed AOMEI was reporting both drives were failing SMART tests and to replace them immediately. I knew this was bogus and that maybe I should change to AHCI from RAID in the BIOS. I followed a post to do this to ensure the machine booted successfully back into Windows. This process worked, and now changing the drive letter worked perfectly. AOMEI also no longer reported the drives failing their SMART tests.Everything is working great except for the performance of my main 1TB m.2 drive. On the other hand, the performance of my 2nd 1TB m.2 drive improved. The drive is still as fast as I'll ever need it to be, but I wondered if anyone has some explanations for this. Below are the CrystalMarkDisk 8 stats of both drives in RAID mode, and then in AHCI mode. Why did the peformance decrease in some areas but improve in others? Because of the AHCI driver? Should I try switching back to RAID mode now that I have the drive letter changed? Another thing to mention is the transfer rate between the 2 drives improved greatly after switching to AHCI mode. Sorry for the long post, but I wanted to try and provide as much detail as possible. RAID MODE Stats (Drives are not in an actual RAID just to be clear) [IMAGE] AHCI MODE Stats [IMAGE] Thanks all for your help!
m15 R4, switched from RAID to AHCI in BIOS, performance decrease