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June 27th, 2017 13:00

Dell M.2 FAQ regarding AHCI vs RAID ON, Storage Drivers, M.2 Lanes, Performance and more

Good day Dell Community,

Over time I’ve received a lot of questions about M.2 drives so I wanted to share some of what I have learned. I will explain in a kind of question/answer format:


What is Dell’s scope of support for the Samsung and Toshiba/OZC NVME drivers posted on these Manufacturers’ websites?
Toshiba/OCZ: (To get the NVME driver select OCZ RD400/400A in the drop down)
Note: Samsung’s explanation of what their NVME driver actually does is on page 22 of the following document:
Keep in mind:
• There exists Dell branded OEM Samsung and Dell branded OEM Toshiba M.2 drives as well as               non-Dell-branded Samsung and non-Dell-branded Toshiba retail drives
• The drivers in question linked above will load for both Dell OEM drives and retail drives alike
• The Samsung and Toshiba/OZC drivers in question can only be used when running in AHCI mode
• These drivers do not apply when running in RAID ON mode as the M.2 drives will be operating under IRST in RAID on mode
Dell does not support the Samsung and Toshiba/OZC drivers for use in AHCI mode. Dell systems with Dell OEM Samsung or Dell OEM Toshiba drives running in AHCI mode will use a Windows inbox driver called stornvme. Stornvme is the driver Dell supports in AHCI mode. Use of the Samsung and Toshiba/OZC drivers will ultimately be decided at end user discretion.

What are some differences between AHCI and RAID ON modes?
Keep in mind:
• Dell systems ship from the factory with the SATA operation mode set to RAID ON
• There exists M.2 SATA and M.2 NVME ( PCIE ) drive types
• Some Dell system models will support both M.2 SATA and M.2 NVME ( PCIE ) drive types while other     Dell system models will only support M.2 SATA drives
• If a Dell system’s M.2 connector supports NVME there will usually be backwards compatibility with         M.2 SATA drives
• The RAID ON controller and AHCI controller each have different hardware IDs and therefore each controller will require different INFs in order to point to other needed files and resources

  -RAID ON drivers = IRST drivers with naming standard iaStorAC
  -AHCI drivers = naming standard iaAHCIC

Dell’s PreOS IRTS and AHCI drivers can both be found in the following package:

Extracted view:

Note: The above downloadable package also has an installer EXE in case you want to update to 15.2 on systems which have an OS already installed.

A new host interface known as NVMe was launched together with Gen 7 (Intel CPU) platforms. This new host interface was built from the ground up for SSD. The host detects on boot up if the storage device is a SATA or PCIe device and then switches the software stack accordingly. Since the host cannot assume all storage devices implement the AHCI host interface the necessary controller is then pushed to the device itself and loaded at boot time. The illustration below describes this.
RAID ON mode: enables the port remapping hardware in the Intel CPU. The remapping hardware is necessary for the Intel RST driver to load the NVMe controller provided by the SSD against the Intel AHCI controller in the CPU. This is required for the Intel RST driver to enumerate NVMe SSD. Also enables support for RAID 0/1/5/10 ( RAID level availability varies by system model ).
AHCI Mode: In this mode NVMe SSDs are enumerated by StorNVMe which is the Windows inbox driver. Implying that in this mode the NVME drive does not work with the motherboard’s AHCI controller, shown in the below illustration:

Below, I have outlined what the storage devices and drives look like in device manager for both M.2 SATA and M.2 PCIE drives, in each operating mode.
M.2 SATA drive when running in IRST RAID ON:

M.2 SATA drive when running in AHCI mode:

M.2 PCIE drive when running in IRST RAID ON:

M.2 PCIE drive when running in AHCI mode:


Is there any performance difference between running an NVME drive in RAID ON mode VS. AHCI mode?
Answer: Based on the explanation on differences between RAID ON and AHCI above, I believe the answer to this is ‘no’. I’ve taken benchmarks below using CrystalDiskMark.
Benchmark Conditions:
• Precision 3510 with a Dell branded Samsung PM951 PCIE 4x drive
• Windows 10Px64 1703 (Creators edition)
• All system drivers updated through Dell Command Update
• One test in RAID ON running IRST 15.2 driver
• One test in AHCI running default stornvme driver
• One test in AHCI testing with Samsung NVME driver
• Power plugged in and all performance and power options at Windows defaults

RAID ON Test results with an NVME drive:

AHCI Stornvme and NVME drive:

AHCI mode with Samsung’s driver:

How can I tell how many lanes my M.2 PCIE drive is running on?
Keep in Mind:
• Some M.2 ports will support only 2 PCIE lanes of bandwidth while other M.2 ports can support 4 PCIE lanes of bandwidth
• The amount of M.2 PCIE lanes a system has available can depend on processor and/or motherboard
• 4 lane capable M.2 drives are typically backwards compatible with 2 lane ports but will suffer performance loss as a result of fewer lanes of bandwidth
You can find out how many lanes a PCIE drive is running by using a program called HWiNFO
Note: Dell does not support this HWiNFO program. This is just a utility I’ve personally found/used and wanted to share.


When I go to the Dell website to purchase a PC I see ‘drive classes’ when selecting an M.2 drive. What does each class mean?
Keep in mind:
• The drive class standard as seen on the Dell website and below, is a storage device identification standard created by Dell
Below is a chart of what each drive class means:

Why can’t I set a hard drive password on my NVME drive?
There are 2 types of M.2 drives. M.2 SATA and M.2 PCIE ( NVME ). HDD password availability for each type is as follows:
M.2 SATA drives are provided hard drive password support from system BIOS.
M.2 PCIE drives are not provided hard drive password support from BIOS. This is working as designed.
Note: M.2 PCIE drives can operate normally even when SATA operation in BIOS is disabled. Hard drive password support is also not provided to M.2 PCIE drives in this mode. (Figure 1)

Where can I find more information if I want to upgrade my Dell to M.2?
The following post contains Dell M.2 / NVME Specifications And Upgrade Requirements For Latitude, XPS, Precision Mobile and Optiplex:
Included in this document you'll find:
• needed part numbers in order to upgrade
• number of total internal drives supported for mentioned models
• how many M.2 PCIE lanes are available on mentioned models

1 Message

December 6th, 2017 20:00

i had this same problem, and after about 8 fresh installs and a few days i've figured it out. i have the toshiba 512 nvme kxg5.

use rufus to make a bootable usb in UEFI GPT partition

go into bios and select RAID

plug in the usb, boot the laptop hit f12 to get into the boot menu

since it's uefi, it'll show up, boot to the usb

go to install windows, and you won't see your ssd. you'll do the load drivers like before, just make sure that the latest drivers are on a seperate usb drive, not the usb stick you are using to install windows. i did this at first, and even though i was able to find them, they wouldn't load. i'd grab the intel rapid storage drivers and console from your dell page, and extract them, no need to run the exe. pick your appropriate windows and bit type.

doing this will use the intel iastora drivers, that will let your ssd actually be recognized as a ssd and it will show up in the storage console like from your pic above.

if you do get it working, i'd stay away from the big feature windows 10 update, it seems to slow the ssd down some.

1 Message

December 7th, 2017 00:00

@DELL-Justin C

I'm having similar issues.  My read and write performance are below what would be expected.

Please let me know how to address this.


4 Operator


783 Posts

December 8th, 2017 11:00


Yes, I have one of those NVME 256GB Toshiba drives on it's way to my test-lab here. If I replicate the 300ish speed I'm sending the drive to engineering and will ask them to comment on it's performance numbers.

Send me a friend request with your service tag. I'll add your tag to the other case I'm working.

9 Posts

December 11th, 2017 05:00

@Dell-Justin C

There are already some benchmarks for Dell 7577 systems online on userbenchmark.

Toshiba KXG50ZNV256G (results from 330 7577):

In comparison to Dell 7577 with Samsung PM961 systems (without any Seq Writes under 1000 MB/s)

In my opinion this seems to be a driver issue. About one year ago there had been already problems with the Toshiba XG4. Some people used the OCZ RD400 driver to increase the Seq Write.

47 Posts

December 14th, 2017 03:00

Hi, I have the same problem: slow write speeds on my Toshiba XG5 256G ( no more than 350MB/s).

I think this could be a firmware issue because of very agressive power-saving settings.

Here is a quote from an article where they talk about Toshiba XG5 SSD :

"Toshiba is coy about the XG5's specifications because ultimately the performance of final products varies by OEM. Performance is also dependent on firmware, which companies can adjust based on their thermal and power requirements. For instance, if a company reduces the 3,000 MB/s sequential read performance to 2,800, it might gain an extra 60 minutes of battery life. Then they could market a model with nine hours of battery life instead of eight."

Source :,5099.html

4 Operator


783 Posts

December 14th, 2017 16:00

@Diken1 and Judge584,

Thank you for your posts and information. I was just speaking with some folks here and they mentioned that: write-cache buffer flushing in Windows is defaulted to 'on' and could be causing the behavior. Using the OCZ driver likely adjusts caching in some way and that could explain the better performance when using that drive.

I did receive a XG5 drive and have duplicated the behavior mentioned in this thread. I have not tried disabling write-cache buffer flushing yet however. I'm going to do that next week and get back with results.

I recommend you turn off Windows write-cache buffer flushing on the device and then see what happens. You can do so by going to device manager, right clicking the drive's properties then:

47 Posts

December 14th, 2017 22:00

Hi Justin,

Write-cache buffer flushing is already deactivated on my side, I did it just after reinstalling Windows 10.

9 Posts

December 15th, 2017 09:00

"I recommend you turn off Windows write-cache buffer flushing on the device and then see what happens." 

This results in strange benchmarks:

Just after boot:

1min later:

Another 1min later:

Results frome someone who changed RAID to AHCI and using stornvme:

47 Posts

December 18th, 2017 08:00

Hi Justin,

Unfortunately it will not solve the problem : write-cache buffer is already deactivated on my xps9360.

By the way I suggest you to also test latest IRST drivers from Intel (v15.8.1.1007), as they provide a little performance improvement over Dell's one and even better : they do reduce coil whine greatly when SSD is under stress with latest 2.4.2 BIOS ;-)

4 Operator


783 Posts

December 18th, 2017 08:00

Thank you for those results Diken1. I'm planning to test my drive again with Windows write-cache buffer flushing turned off and will get back with results.

4 Operator


783 Posts

December 18th, 2017 09:00

Hi Judge584,

I assumed it wouldn't solve it, just doing my due diligence :)

I'm running on WIN10 with write-cache buffer set to off. I have maintained replication of the performance numbers, as we expected. Below is my latest test:

I will test out to see what happens.

3 Posts

December 18th, 2017 20:00

1 Message

December 18th, 2017 21:00

Just got a 7577 with 256GB NVME and 1TB Hard Drive. Took out the hard drive and replaced it with my 1TB Samsung 840 evo SSD. The Samsung Magician software wasn't fully functional and saw that the bios was set to raid and not AHCI. Are there any long term performance or reliability reasons that I should switch over to AHCI from the raid? I'll just leave it as is if there shouldn't be any issues.

47 Posts

December 19th, 2017 10:00

Hi Justin, I have news: please find below latest tests results

Config : XPS 13 9360 i5-8250u 8GB ram and with Toshiba XG5 256GB PCIE-Nvme

Bios: 2.4.2

Bios mode : RAID

IRST Drivers : latest from Intel website : version

First run after windows boot :

Second run 1 second after first one :

Third run 5 minutes after second run:

4 Operator


783 Posts

December 19th, 2017 10:00


Thank you for your testing and feedback. I did more replication attempts yesterday as well and I've consistently re-produced the behavior, including on The drive is going to Dell engineering at this point.

My next step is to simply wait for engineering to get back with me on why this drive is performing this way. I will be back to delivered any results I obtain in the future. No ETA right now.

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