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#76 RE: Samsung SM951 AHCI not reaching full speed by Lebedev 25.03.2018 14:19

Zitat von agentx007 im Beitrag #74
@Lebedev There is a problem with your "SATA controller on SM951 PCB" theory :
There are no SATA specs for over 600MB/s transfers.
SM951 type drive (regardless of protocol used or capacity) can do 2GB/s Reads, and 128GB model contains two memory chips/ICs on it's PCB.
That's WAY beyond any SATA device can do in theory - which means, those SM951 drives are NOT SATA devices, and they cannot contain/utilise any SATA related hardware.
You probably know that there are multiple NAND ICs placed on most SSDs. As far a i know (that's what i have heard), usually all of them are organised in a Raid 0 simillar system. That's where the high speed SSD performance comes from. This is the reason why i don't see any conflict with the conclusion, that the SM951 is a SATA device. For example, you could also take six regular SATA SSD, and connect them to your intel onboard SATA controller and create a Raid 0 which would result in max. 3600MB/s.

However, i know the 600MB/s limit, but i think it's more a limit of the physicall SATA interface and cables, not of the used AHCI protocoll. On the SM951 you have no physical interfaces or cables used, just ultra short conducting paths. The 600MB/s limit can probably be ignored here, as long as all ICs can go faster.

Zitat von agentx007 im Beitrag #74
Both SATA and PCI-e drives can use AHCI protocol, however that's end of similarities between them.
In short : It's a square and a rectangle type of stuff (SATA == AHCI or "IDE" or RAID, AHCI =/= SATA).
AHCI, IDE and RAID are in this case just modes of the SATA Controller. If you put it in RAID Mode, AHCI is still used. The only difference ist, that the Option Rom (RAID Bios) is enabled. I didn't say that AHCI == SATA.

Zitat von agentx007 im Beitrag #74
PS. If using AHCI M-key M.2 was so easy, I woudn't have to use Clover/DUET to boot from it on legacy hardware (which supports SATA booting from PCI-e add-on cards since 2004/2005) :)
The decisive point is a option ROM. If the PCIe card does not have a option ROM, the "booting from PCI-e add-on cards" is useless. An Option Rom is the solution, that the Mainboard BIOS/EFI does not have to have any special drivers for a device, and you can still use them as bootdevice.

#77 RE: Samsung SM951 AHCI not reaching full speed by agentx007 25.03.2018 15:51

Zitat von Lebedev im Beitrag #76
You probably know that there are multiple NAND ICs placed on most SSDs. As far a i know (that's what i have heard), usually all of them are organised in a Raid 0 simillar system. That's where the high speed SSD performance comes from.

However, i know the 600MB/s limit, but i think it's more a limit of the physicall SATA interface and cables, not of the used AHCI protocoll. On the SM951 you have no physical interfaces or cables used, just ultra short conducting paths. The 600MB/s limit can probably be ignored here, as long as all ICs can go faster.
You can have multple ICs on PCB in SSD - true.
However, M.2 drives can't have many of those because there is simply no space for them.
Regardless... You want me to belive NAND memory are linked to controller using SATA-like interface ?
Or is controller connected to PCIe via "SATA"-type interface ?
Because both NVMe and AHCI SM951 drives clearly use the same controller as stated in this review : LINK

Zitat
The same Samsung three-core UBX controller is used on both SSDs.
...
The same low-power DDR2 DRAM is also used on both 256GB parts.
...
We took a picture of the back of the drives to show that this capacity size is single-sided. But in doing so, we noticed that one drive was a little taller. After investigating further, we discovered different flash. The SM951 AHCI uses an eight-die stack (per Samsung's NAND flash decoder) and the SM951-NVMe uses a 16-die stack.
...
For the most part, though, the flash is the same other than its die density and the number of dies in each package.

PS. RAID0 on regular SATA drives will be limited by chipset DMI interface in Intel's case, and CPU to Chipset PCI-e connection on AM4/TR4 (AMD), both of which aren't used for SATA-only devices.
That's why, so many early M.2 supporting boards can't reach max. performance of PCI-e 3.0 x4 M.2 drives.

#78 RE: Samsung SM951 AHCI not reaching full speed by Lebedev 28.03.2018 23:56


http://www.t13.org/documents/UploadedDoc...t_-_2_ACS-2.pdf

https://en.wikipedia.org/wiki/Advanced_H...oller_Interface

Zitat
The Advanced Host Controller Interface (AHCI) is a technical standard defined by Intel that specifies the operation of Serial ATA (SATA) host bus adapters in a non-implementation-specific manner.


As you can see, this SSD uses SATA interface. As i already said, the SM951 is recognized as a SATA class device. The communication between SSD and mainboard does not use the SATA interface, it uses PCIe. The communication between NAND chips and controller cannot be SATA too, because if it would be, were able to see every NAND chip is a single drive. And here we are at the point again: the controller on the SM951 consists logically of two controllers. One SATA Controller (PCIe to SATA bridge), and one disk controller (uses SATA interface for communication to first controller). The disk controller is responsible for controlling the NAND flash chips. The proof for this theory is, that two devices appear in the device manager if you insert a SM951 SSD. One disk, and one storage controller.

Yes, i know, there is only one controller on the SM951, but logically it's two.

#79 RE: Samsung SM951 AHCI not reaching full speed by Fernando 29.03.2018 00:09

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@Lebedev:
The OS Device Management detects all kinds of hardware, which are connected to the system.
Why does the Device Manager not list any Disk Controller and why do the manufacturers of such devices not offer any driver to support them? Maybe because such Controllers do not exist.

#80 RE: Samsung SM951 AHCI not reaching full speed by Lebedev 29.03.2018 00:21

Hardware ID of the storage controller: VEN_144D&DEV_A801
klick here for details about vendor id 144D

It's both Samsung. I don't have any other samsung device inside my computer. I have an Asus P9X79 Pro Mainboard with Intel X79 Chipset. The Intel onboard chipset is the only other storage controller besides my two SM951 SSDs.

seriously: you said by yourself that the SM951 SSD uses the AHCI protocoll. Look what i linked:
https://en.wikipedia.org/wiki/Advanced_H...oller_Interface

Zitat
AHCI is a technical standard defined by Intel that specifies the operation of Serial ATA (SATA) host bus adapters

Can you explain to me how to attach an AHCI capable storage device directly via PCI Express? There MUST be a SATA Controller in between. Do you think that AIDA64 is lying?

EDIT by Fernando: Last posts merged and inserted pictures resized (to save space)

#81 RE: Samsung SM951 AHCI not reaching full speed by Fernando 29.03.2018 00:47

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Zitat von Lebedev im Beitrag #80
Can you explain to me how to attach an AHCI capable storage device directly via PCI Express? There MUST be a SATA Controller in between.
There is defnitively a SATA AHCI Controller in between. The related HardwareIDs are within the picture you have just posted.

#82 RE: Samsung SM951 AHCI not reaching full speed by Lebedev 29.03.2018 00:51

Nice, so now you agree that it's a SATA device. Do you also agree that this SATA Controller is inside the SSD?

#83 RE: Samsung SM951 AHCI not reaching full speed by Fernando 29.03.2018 01:21

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Zitat von Lebedev im Beitrag #82
Nice, so now you agree that it's a SATA device. Do you also agree that this SATA Controller is inside the SSD?
I never had a doubt about it, but a SATA Controller is not a Disk Controller.

#84 RE: Samsung SM951 AHCI not reaching full speed by 100PIER 29.03.2018 09:25

@Lebedev
The performances I get with SM951 AHCI 512GB plugged on PCIe Gen 3 are quite good:

Meltdown/Spectre protection disabled:


Meltdown/Spectre protection enabled:


When plugged on a PCIe Gen 2 instead of Gen 3 the performance is obviously low:

#85 RE: Samsung SM951 AHCI not reaching full speed by Lebedev 29.03.2018 20:52

Zitat von Fernando im Beitrag #83
I never had a doubt about it, but a SATA Controller is not a Disk Controller.
I didn't say that anywhere. But you can't connect multiple NAND flash chips to a SATA controller. You can't connect a spinning hard drive to a SATA controller. There's always i disk controller in between, which controlls the NAND chips or the Platter+Head. Do you agree on that?

#86 RE: Samsung SM951 AHCI not reaching full speed by Fernando 29.03.2018 21:05

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Zitat von Lebedev im Beitrag #85
You can't connect a spinning hard drive to a SATA controller. There's always i disk controller in between, which controlls the NAND chips or the Platter+Head. Do you agree on that?
No, unless you show me the additional Disk Controller listed within the Device Manager.

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