RAID help on Z97 Extreme6

The ASMedia SATA controllers, two on your board, do not support RAID. They are completely independent of the Intel SATA controller.

You have nothing to worry about using RAID mode in terms of losing AHCI features. All the features provided by AHCI mode are also provided in RAID mode, whether or not the drives are in a RAID array.

Intel calls AHCI mode a "subset" of RAID mode, when describing their RAID support. Drives in a RAID array still use AHCI features.

You can set the SATA mode to RAID in the UEFI/BIOS, and have a drive connected to each of the six Intel SATA ports but have none of them in a RAID array. That results in each drive operating in AHCI mode.

While we still have an IDE option for the SATA mode in the UEFI on Z97 boards (why, who would use it?), using RAID mode does not put the drives on an Intel SATA controller that are not part of a RAID array into IDE mode. It has been that way since the days of Intel Matrix RAID, used with the Intel ICHx series SATA controllers.

Intel designed the AHCI feature set with a HDD manufacture, originally to improve HDD performance. Ironically, AHCI features are better suited for use with SSDs. Neither SATA or AHCI were originally designed with SSDs in mind, and we now finally have a new storage protocol designed for flash storage, NVMe.

Also, you don't want to connect any of your SSDs to the ASMedia SATA controllers... don't get me started on that...

Well... Ok.

The problem with the ASMedia SATA chipset, and most of the similar Marvell SATA chipsets, is they are designed to be connected to one PCIe 2.0 lane provided by the main chipset on a mother board.

The maximum date rate of one PCIe 2.0 lane is 5Gb/s (that's 5 Giga-bits per second). The standard SATA III specification is a 6Gb/s maximum data rate connection. The Intel SATA III chipsets provide a full 6Gb/s connection.

Obviously, 5Gb/s is not the full bandwidth of the SATA III specification. Given that, these SATA chips should not be able to perform as well as the Intel SATA III interface does. Simply put, they don't.

These SATA chipsets have been called "SATA III" for years. Why that is allowed I don't understand. If SATA III is based on a 6Gb/s interface, how does a 5Gb/s interface qualify as SATA III? Simply because it is beyond SATA II (which is a 3Gb/s interface)?

To be fair, these add-on SATA chipsets were designed for a purpose: to supply extra SATA ports for a mother board (either built in or on an add in card) while working with the limited resources available to them on a PC mother board.

The best we've had until the Intel 100 series chipsets is PCIe 2.0 lanes. The Intel 100 series chipsets like a Z170 have PCIe 3.0 equivalent speed data lanes, but are all used by the Ultra M.2 slots and the Intel SATA III ports. These Intel chipsets also provide PCIe 2.0 lanes, which are still being used by the ASMedia and Marvell SATA chips.

So their performance with SSDs is less than the Intel SATA III interface, but by how much and does that really matter? In these examples, the board I was using had a Marvell "SATA III" chipset, but the ASMedia chipset performs the same. This is an older Samsung 830 SSD, highly regarded when it was released. First a benchmark on the Marvell chipset, and then the Intel SATA III chipset, same mother board, etc:





The Intel chipset is using a different driver than the Marvell chipset, we can see iaStor just above 1024 K - OK, in the second picture, identifying the Intel RAID driver (what a coincidence) and Intel SATA chipset.

Another thing I noticed recently, is when I was trying to use the ASMedia chipset on my Z170 board with Windows 10. I had a Samsung 840 SSD on the ASMedia chipset, trying an ASMedia SATA driver. I tried running the "optimize" feature for SSDs, available on Windows 8 - 10, a manual TRIM on the entire free space on an SSD. I've done that many times on the Intel SATA interface, even on RAID 0 arrays of SSDs, and with NVMe SSDs. Always works fine.

But not that time, the TRIM process never finished. I can't recall all the details now, but it was not good. Does that result tell us that the TRIM command is not supported by the ASMedia driver and chipset combination? I'm not able to say no with my one experience, but given my other experiences with that feature, it is not a good sign at all.