[SOLVED] Linking 8-ports (2x SFF-8087) to Supermicro SAS2 Backplane for 48 Gb/s?

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eduncan911

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How would you "link" 2x SFF-8087 connectors, 4-ports each/8-ports total, to the Supermicro SAS2 SFF-8087 backplane - that has a single Expander chip - to double the 24 Gb/s to 48 Gb/s?

Is there any special configuration I need to do on the LSI drivers, in Linux? The expander chip is LSI as well as the LSI 9211-8i.

Not talking about 2x HBAs for Multi-Path. That's only available in the EL2 models.

Apparently it is possible with the EL1, single expander chip models via some sort of "8-lane linking" (see below) with two SFF-8087 cables to a single HBA.

/TL;DR

So, I've researched this for too many years (8+) and always landed on, "I can only use one SFF-8087 cable, with 4-ports, from my HBA to the backplane. That's a maximum of 24Gbps." It's the SAS2 SFF-8087 backplane, BPN-SAS2-846EL1 - one single expander chip.

Again, today I was searching during a rebuild - since I will be adding dual-40 Gb/s QSFP+ to this box because, come on, I have to be able to use those two extra SFF-8087 connectors somehow.

Then I ran across this website which mentions something I have never read before:

With typical 8 lanes HBA or controller, 48Gb/s board to controller bandwidth is enough for...(snip)
And...

With typical 8 lanes HBA and controller and two SAS cable from the backplane, the maximum speed is 48Gb/s.
Wait, what?!?

The manual mentions nothing like this: https://fuzhaopeng.files.wordpress.com/2020/03/bpn-sas2-846el.pdf

I searched and bit more and found one person that claims to have tested linking all 8-ports to the SAS2 backplane; but, "it didn't work all that well for me." That's was the most I got out of the old thread.

So, the BPN-SAS2-846EL1 backplane in the Supermicro SC846 chassis has 3x SFF-8087 ports, and the manual lists all three as Primary.

Would anyone know how to link 8x ports, with dual SFF-8087 cables, to this backplane?

Is it as simple as plugging in two cables, and "poof", you have 48 Gb/s?

I have 10+ Enterprise SATA3 SSDs I can test this with that all peg the 540 MB/s bandwidth of SATA3. So a RAID0/ZRAID0 should yield around 50 Gb/s.

I just need some pointers for how to configure this. Running Linux/Debian.
 
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eduncan911

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Ah, found "the" post that proves it!!!


Woohoo! Nothing to do but just connect the two cables.

Also, you can use the 3rd SFF-8087 port to connect a breakout cable - and connect an additional 4 drives for a total of 28 drives from a single 8-port HBA, with 48 Gb/s bandwidth!

Sweet! As I have several of those break-out cables too!

EDIT: Doh, my LSI 9211-8i is an PCIe 2.0 x8-lane card. That's a maximum of 8 * 500MB/s (PCIe 2.0 lane speed) = 4 GB/s, or 32 Gb/s.

Time for a PCIe 3.0 card!
 
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gregsachs

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One bit about doing this, at least with the intel/LSI expanders, and likely with others, is that it works as a waterfall connection-all traffic goes over one cable until you exceed that port's limit, when it spills over to the second port. That could give you very odd effects if you have a flaky cable on the second connection...
 
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eduncan911

The New James Dean
Jul 27, 2015
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One bit about doing this, at least with the intel/LSI expanders, and likely with others, is that it works as a waterfall connection-all traffic goes over one cable until you exceed that port's limit, when it spills over to the second port. That could give you very odd effects if you have a flaky cable on the second connection...
You know, I've had all of this setup on a test bench for a few months but been busy with life. I could actually test this ...

I did verify that a single connection limits of SAS2 can easily be hit by a few SSDs. So I should be able to replicate that.

An interesting article. I'll read it more in depth when I start to test it.
 

eduncan911

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Is this the same chip in the LSI backplanes?

Quote from article that basically says two connections:

For most situations, using the two SFF-8087 connectors from an Intel RAID Controller to the Intel RAID Expander RES2SV240 is more than what an average situation requires. In theory, up to 48 Gb/s data transfer (eight ports x 6 Gb/s).