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SAS Controller Questions

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I currently have 3 SAS2LP controllers that tie into my Norco 4224 backplanes, but the new motherboard I have only has 3 x16 and 1 x1 PCIE slots. I am hoping to add a 10GB NIC, and possibly a transcoding video card down the road. I have bought a RES25V240 which I've seen I don't even need to mount in a PCIE slot which is kinda cool, but I am wondering what sort of throughput I am going to see if I use that. Given that I still need 1 HBA I am assuming I'd remove 2 SAS2LP, and have one with a direct connection to a backplane and the other to the RES24V240 with it's other 5 ports connecting to the other backplanes.


Essentially I want to try and understand the following:

1) Am I going to significantly impact performance with 5 backplanes going through the one card. I currently get around 95-98MB/s for Parity Checks and dont' know if this will really impact that, or if I have 8-10 people streaming off different disks am I going to bottleneck at all

2) Is there a significant difference between running 1 SAS2LP with 5 connections through the RES25V240 vs running 2 SAS2LP cards both feeding a connection into the RES25V240 card and only using 4 connections from that to backplanes

3) Given that the backplanes are all 6GB SAS, is there any value in buying a 12GB SAS controller with 6 ports and run SFF-8643 to SFF-8087 converting cables? I've had one vendor tell me this could cause issues (i.e. frying backplanes), but I dont' know if that's true, or if I'd see any improved performance vs the SAS Expander... If so, this would also potentially set me up if I was to replace the case down the road as I could get one with 12GB SAS (though these are really expensive)

4) Would I even notice much difference between 6GB SAS and 12GB SAS with all WD Red drives? I know this gets into a throughput question, and I've seen some comments on other threads, but I'm still not clear on if there is a significant gain by going to 12GB SAS (enough to justify a $500 card and $1200-$1500 case down the road)


Any input or thoughts would be appreciated.

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IIRC the SAS2LP doesn't perform very well with an expander, they are also not recommended for Unraid for a long time now, the expander works very well with an LSI HBA, you can see some performance numbers here.

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