CSE-847 questions

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asgardthor

New Member
Jan 24, 2020
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Hello!

I've recently purchased a CSE-847 36bay SAS 3back plane.
It comes with the following two back planes. I'm currently building out an epyc server to replace a 1950x build. While deciding on motherboards, I've come across the SM H12ssl-c, which has two SAS3 ports. This was tempting since it will save $100ish would go to a SAS3 card, and save a slot. But after reviewing the SM CSE-847 manual. I've across different ways to connect the two back planes together.
847.jpg

I will not need to use external SAS, everything will be internal. Would using a single SAS cable per backplane limit any performance?
BPN-SAS3-846EL1
BPN-SAS3-826EL1

OS: Truenas
Drives - WD Red's
 

i386

Well-Known Member
Mar 18, 2016
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I would cascade the backplanes: two cables from hba/raid controller to BPN-SAS3-846EL1 and two cables between BPN-SAS3-846EL1 and BPN-SAS3-826EL1
Would using a single SAS cable per backplane limit any performance?
Hdds? no
Ssds? It depends :D
 

asgardthor

New Member
Jan 24, 2020
8
4
3
I would cascade the backplanes: two cables from hba/raid controller to BPN-SAS3-846EL1 and two cables between BPN-SAS3-846EL1 and BPN-SAS3-826EL1

Hdds? no
Ssds? It depends :D
So with your suggestion, I would still only need two sas ports on my HBA. Sounds like a good idea
 

mattventura

Active Member
Nov 9, 2022
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That image isn't the same backplane you have. The BPN-SAS3-826EL1 has four SAS x4 ports, so you can have a x8 link from the HBA to the first backplane, and an x8 link from the first backplane to the second.

As for whether it will limit performance, it depends on the drives. SSDs will bottleneck quite quickly (you basically want 1 lane per SSD), whereas HDDs are a lot slower so it takes many more drives before it becomes an issue. Depends on the drives, but somewhere around 6 drives per lane is probably fine. If you fill up the whole chassis with HDDs, that x8 12gb link will likely be okay, but as soon as you start adding SSDs, you might need to change it up a bit. It also depends on access patterns - if all the drives are part of one big array and thus are more likely to be accessed simultaneously, then it's a bigger issue. If they're being used as multiple independent drives/arrays, it's less of an issue.
 

asgardthor

New Member
Jan 24, 2020
8
4
3
That image isn't the same backplane you have. The BPN-SAS3-826EL1 has four SAS x4 ports, so you can have a x8 link from the HBA to the first backplane, and an x8 link from the first backplane to the second.

As for whether it will limit performance, it depends on the drives. SSDs will bottleneck quite quickly (you basically want 1 lane per SSD), whereas HDDs are a lot slower so it takes many more drives before it becomes an issue. Depends on the drives, but somewhere around 6 drives per lane is probably fine. If you fill up the whole chassis with HDDs, that x8 12gb link will likely be okay, but as soon as you start adding SSDs, you might need to change it up a bit. It also depends on access patterns - if all the drives are part of one big array and thus are more likely to be accessed simultaneously, then it's a bigger issue. If they're being used as multiple independent drives/arrays, it's less of an issue.
Appreciate the information! Looks like that is the path I will go. NVME and sata SSD's will be in plugged in directly to the motherboard.