Backplane connection (BPN-SAS2-EL1) questions

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marirs

New Member
Mar 11, 2018
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I've acquired a Supermicro SC847 system, and my current project is to quiet it down and reduce its power usage. The server came with 2 LSI HBA connected with 2 cables each to the front and rear backplanes.


Does this look right? According to the manual the two ports are Primary SAS connector: PRI_J1, and PRI_J2 (PRI_J0 is the one on the far right). Does having two cables connected to the same HBA increase the available bandwidth? Will I be ok with just one cable connected to PRI_J0?

Also, to reduce heat and power use would it be possible to remove the LSI HBA and use the SAS connector on the motherboard? The motherboard is the Supermicro X9DRI-LN4F+, which has a SAS connector from the Intel C602 SB I think.

Furthermore, if the above would work, can I use a reverse breakout cable and use 4 SATA ports from the motherboard to connect to the rear backplane, thus eliminating the need for both LSI HBAs?

The server is for media storage, so I don't need super high throughput. I will be using OMV / SnapRaid, and there will only be 1-2 users.
 

marirs

New Member
Mar 11, 2018
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ok, some more searching and I found this post which answers my first question. So it doesn't sound like I will benefit much from having dual links from the HBA to the backplane. I will attempt to switch to the motherboard SAS port and see what happens.

The only remaining question is the use of the reverse breakout cable...
 

Aestr

Well-Known Member
Oct 22, 2014
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The X9DRI-LN4F+ does not appear to have a SAS controller looking at the specs page. Likely what you're mistaking for SAS is the SFF-8087 port that provides an additional 4 SATA ports.

Also you can't connect SATA ports from a motherboard or a controller to a SAS expander backplane as SATA can't understand the shared links of the expander. This is different than using SATA drives connectoed to the expander as it can communicate to SATA drives without any additional functionality required.
 

marirs

New Member
Mar 11, 2018
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Ah, ok thanks that makes it a lot clearer.

This is what the manual says
Eight Storage Control Unit (SCU) SAS/SATA2 Ports
(SCU 0~3, 4~7) are located on the X9DR3-LN4F+,
and four SCU SATA2 ports (SCU 0~3) are on the
X9DRi-LN4F+ to provide serial link connections.
I didn't quite understand the distinction until you pointed it out. It sounds like the X9DR3-LN4F+ would do what I wanted, while the X9DRI-LN4F+ will not. Also I think I'm a bit clearer on the reverse breakout cables. It will work with a backplane that doesn't use an expander (just straight 1-1), but not one with an expander.

edit: so I guess the best I can currently do is get rid of one of the LSI HBAs, leaving on HBA for the two backplanes.
 

Aestr

Well-Known Member
Oct 22, 2014
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386
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Seattle
Reverse breakout cables will work with direct connect backplanes like you mentioned. They are also used to connect an expander backplane to a controller that uses individual ports instead of a combined one. They aren't that common and generally you see them on motherboards rather than AICs. A good example is the X10SL7-F.