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ML10 V2 PCIe slot speeds


iandrews
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I was building up my ML10 V2 at the weekend, moving disks and the M1015 card from my Gen 8 to it. The M1015 is a PCIe 2.0 X8 card, I knew the X16 slot only ran at X8 speed, so thought I would just double check the others, and it appears the PCIe 2.0 x8 and x4 slots only run at X1 speed. 

 

From the ML10 V2 guide: http://www8.hp.com/h20195/v2/GetPDF.aspx/c04567802.pdf
 
Expansion Slots
 
Expansion Slot #     Technology     Bus Width*     Connector Width     Form Factor     Notes
 
4     PCIe 3.0     X8     X16     Full Length/Full Height
3     PCIe 3.0     X8     X8       Full Length/Full Height
2     PCIe 2.0     X1     x8        Full Length/Full Height
1     PCIe 2.0     X1     X4       Half Length/FullHeight

*Indicates the number of physical electrical lanes running to the connector.

 

So, where as I was going to put the card into slot 2, it has to go into slot 3 or 4 using up one of the PCIe 3.0 slots (not that I currently have any need for them). 

 

I also have a NC360T dual NIC card X4 that I was going to install (to be the in and out ports to a Untangle VM). So again, that will need to go into the other PCIe 3 slot. Though I have read it will work at X1 speed, and seeing as my Broadband connection is about 35Mbps up 10Mbps down I assume the drop to X1 speed form X4 won't make a difference.

 

Seems a bit cheeky of HP to only have one of the slots running at the "correct" speed.

 

So, if you are installing any cards, just check you are putting it in a slot that can handle the speed.

 

  

 

 

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The CPU/chip-set determines the number and type of PCIe lanes available. The on board NIC uses some lanes. Most likely uses for the two slots running x8 lanes each are RAID controllers or quad Gigabit or dual 10Gb NIC's. A dual port Gigabit NIC that supports PCIe 2.0 will run fine on x1 lanes. The HP 332T is a x1 PCIe 2.0 NIC. I think they give you larger slots with lesser lanes is to at least give you a place to use older cards. They may not run full speed, but you can still use them. A x1 PCIe 1.0 lane runs at 2Gb/s or 2.5GT/s. A x1 PCIe 2.0 lane runs at 4Gb/s or 5GT/s.

Your NC360T is x4 PCIe 1.0 so running it in slot 1 or 2 in the ML10v2 it will run at x1 PCIe 1.0 speed. Theoretically a Gigabit Ethernet port is capable of transfering data full duplex at 1Gb/s in each direction 2Gb/s per port and two ports for 4Gb/s for the NIC. Ethernet does not work that way. In general, (this is when the argument starts) Gigabit Ethernet connections tend to run around 125MB/s two ports 250MB/s or 2Gb/s. I do not think you will see a performance hit running the NC360T in either of the x1 slots. Watch for HP 332T NICs or x1 NICs based on BCM5720.

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I was building up my ML10 V2 at the weekend, moving disks and the M1015 card from my Gen 8 to it. The M1015 is a PCIe 2.0 X8 card, I knew the X16 slot only ran at X8 speed, so thought I would just double check the others, and it appears the PCIe 2.0 x8 and x4 slots only run at X1 speed.

It is because the PCIe 2.0 slots are coming from the Intel chipset whilst the PCIe 3.0 slots are coming direct from the CPU. The block diagram explains it more clearly. It is just a limitation of the CPU and chipset.

 

I also have a NC360T dual NIC card X4 that I was going to install (to be the in and out ports to a Untangle VM). So again, that will need to go into the other PCIe 3 slot. Though I have read it will work at X1 speed, and seeing as my Broadband connection is about 35Mbps up 10Mbps down I assume the drop to X1 speed form X4 won't make a difference.

PCIe 2.0 x1 is capable of 500MB/s so more than enough for your NIC.

 

PCIe 3.0 x1 is just under 1GB/s. They changed the encoding method so even though the speed has doubled, the actual throughput is slightly less than double.

 

Your M1015 controller is PCIe 2.0 x8 so 4GB/s. You won't gain any benefit of PCIe 3.0 even though the slot is capable of it but it is the only way to exceed 500MB/s on the ML10v2.

 

Seems a bit cheeky of HP to only have one of the slots running at the "correct" speed.

The speed is actually correct. The only thing differing is the number of data lanes connected as most devices will just negotiate to use whatever is available. Differing number of actual lanes and physical width of the slot is fairly normal. It is clearly stated in the datasheet anyway so they're not attempting to mislead you.
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Thanks guys. That block diagram helps explain it. So as it stands (and as I put it in) I need the M1015 in one of the x8 slots, and I could either put the NC360t in the other x8 slot, or (as I won't be pushing it to full speed) one of the x1 slots.

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So as it stands (and as I put it in) I need the M1015 in one of the x8 slots, and I could either put the NC360t in the other x8 slot, or (as I won't be pushing it to full speed) one of the x1 slots.

Yes to the M1015.

 

Ah wait. Your NC360t is only PCIe 1.0. I thought it was PCIe 2.0. It won't matter with your specific case but you're likely to get slightly bottlenecked by the PCIe bus since PCIe 1.0 x1 is 250MB/s. You're only going to notice it if you're running both Ethernet interfaces at full speed though.

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They changed the encoding method so even though the speed has doubled, the actual throughput is slightly less than double.

 

 

 

 

PCI Express 2x has 20% overhead

PCI Express 3 has 1.54% overhead

 

500 throughput / 985 throughput

Edited by Shonk
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I plan on doing the HP SmartArray P222 in one slot, and an Intel ET dual-port Gig NIC in another.  That's all I plan to add for expansion cards.

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