I don't understand how motherboards work and I'm hoping for good news - MSI Z690 Edge Wi-Fi DDR4 + LSI 9207-8i + PCIe questions.

[accelaptd]

I've put this here rather than in Hardware as I think my question is ultimately about HBA and storage bandwidth rather than motherboards but if someone with the authority to move it disagrees, please do as you will. The TL;DR is in yellow.

 

I am really hoping someone who understands this stuff better than I do can tell me how accurate my own understanding of this situation is and what is wrong with it. I went to art college and it's a miracle I'm as competent with computers as I am and in this case I need reassuring or warning.

 

Here is my board, and its spec sheet and manual. It is housing an i7-12700K and the HBA I have purchased is the LSI SAS 9207-8i.

 

I wanted one of the Z690 boards where the 5.0 lanes feed two x16 slots that can go 5.0 x16/x0 or 5.0 x8/5.0 x8 as this meant I didn't have to try and work out the answers to the first questions I'm asking here but the extra cost of the board plus sinking money into early adopter DDR5 sticks was very off-putting when I already have a more than suitable DDR4 kit for my needs and the only DDR4 version with that config isn't easily available here.

 

As the 9207-8i is a PCIe 3.0 x8 device it would be obvious that it would be completely happy in either of the 5.0 x8 slots on the boards I didn't buy and the single 5.0 x16 on the one I did. 

 

Here is the PCIe offering I have to work with:

 

Quote

3x PCIe x16 slots

    PCI_E1 slot (From CPU)

       - Supports PCIe 5.0 x16 

    PCI_E3 & PCI_E4 slots (From Z690 chipset)

       - Supports PCIe 3.0 x4

1x PCIe 3.0 x1 slot (From Z690 chipset)

 

...in addition to....

 

Quote

4 x SATA 6Gb/s ports

     SATA5~8 (From Z690 Chipset)

 

2 x SATA 6Gb/s ports 

     SATAA~B (From ASMedia ASM1061)

 

4x M.2 slots (Key M)

     M2_1 slot (From CPU)

          Supports PCIe 4.0 x4

          Supports 2260/ 2280/ 22110 storage devices

     M2_2 slot (From Z690 Chipset)

          Supports PCIe 4.0 x4

          Supports 2260/ 2280 storage devices

     M2_3 slot (From Z690 Chipset)

          Supports PCIe 4.0 x4

          Supports SATA 6Gb/s

          Supports 2242/ 2260/ 2280 storage devices

     M2_4 slot (From Z690 Chipset)

          Supports PCIe 4.0 x4

          Supports SATA 6Gb/s

          Supports 2242/ 2260/ 2280 storage devices

 

.... should this become relevant as I gained enough from reading the chipset spec and looking at the diagram that these things all use essentially the same resources to eventually reach the CPU/chipset.

 

I had initially thought I'd need the 9207-8i in PCI_E1 and then I'd need to find a pair of -4i cards to occupy PCI_E3 and PCI_E4 if I wanted to have the headroom to reach "... in a desktop case? really?" levels of HDDs eventually.

 

I dug a little deeper and started to make assumptions. Say I just put the 9207_8i in PCI_E3. It's an x16 slot so it physically fits, but the 9207-8i is going to have access to half of the 3.0 bandwidth its form factor and spec sheet say it wants. That's going to suck, surely?

 

The 9207-8i is in the HBA speed test thread:

 

Quote

LSI 9207-8i PCIe gen3 x8 (4800MB/s) - 9w - LSI 2308 chipset

8 x 565MB/s

 

At absolute peak capacity it can use 4520 MB/s of bandwidth. I note a similar number on section 3.2 of the 9207-8i manual. I'm led to believe that 3.0 x4 is worth 4000 MB/s and 3.0 x8 is worth 8000MB/s, so at absolute peak capacity 9207-8i is only using ~12.5% of the extra bandwidth that the step from 3.0 x4 to 3.0 x8 affords it. Furthermore, I'm using HDDs that are quoted at 259MB/s transfer speed so even if I have the full 8 drives running at full speed at once that's only 2072MB/s and comfortably under the 3.0 x4 bandwidth ceiling.

 

It's probably suboptimal but also basically fine to be running my 9207-8i chock full of comparatively slow rusty ol' HDDs in a PCIe slot with 3.0 x4 of bandwidth rather than 3.0 x8 of bandwidth, right?

 

If this follows then I can run a 9207-8i in each of PCI_E3 and PCI_E4 and suddenly I can add in the same number of SATA ports through the HBAs but I have my PCI_E1 slot back which is pretty exciting because I'm currently using one of the passively cooled GT710s and I'm looking at an RTX 3080 shaped gap.

 

Am I tempting the wrath of dark forces by not knowing the meaning of the cryptic motherboard input/output capacity runes and foolishly thinking I can wield the power of 4 cutting edge 4.0 x4 M.2 SSDs, up to 22 SATA ports and a current generation flagship GPU in the same low-to-mid-end desktop motherboard without consequences? Because that seems too good to be true and I've seen enough people sharing their experiences of using certain M.2 slots turning other features off that it has me paranoid.

 

 

....and a bonus thing I've been wondering about while I have your attention:

 

Do I put my parity drive in the HBA with the rest of my spinning HDDs or is there any advantage to giving it a motherboard SATA port with my SATA SSDs?

[JorgeB]

33 minutes ago, accelaptd said:

I'm led to believe that 3.0 x4 is worth 4000 MB/s

That's the theoretical max, actual max is around 3400MB/s, should be similar to the 9300-8i in that situation, still more than enough for 8 HDDs.

 

37 minutes ago, accelaptd said:

If this follows then I can run a 9207-8i in each of PCI_E3 and PCI_E4 and suddenly I can add in the same number of SATA ports through the HBAs but I have my PCI_E1 slot back which is pretty exciting because I'm currently using one of the passively cooled GT710s and I'm looking at an RTX 3080 shaped gap.

Yes, just keep in mind that those slots go through the DMI, together with the onboard SATA ports/most M.2 slots, so bandwidth is shared, unlike the x16 CPU slot and M.2 slot 1 that go directly to the CPU, but since DMI for Z690 is PCIe 4.0 x8 it should be fine for all you need.

 

 

 

[JonathanM]

Just an FYI, your post is rather unreadable for a fair number of folks because you got fancy with your text.

[ChatNoir]

Works fine on dark theme, but I see how it looks bad on the light one.