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I have got a chassis with the Supermicro BPN-SAS3-826EL1 backplane. This backplane allows 12 HDDs to be attached. However, I obviously haven't yet understood the cabling between the HBA and the backplane which I need to actually use all 12 HDD ports.

According to the first drawing on page 3-1 in the manual, PRI-J1 and PRI-J2 should be connected to the HBA (and thus are "inputs"), while PRI-J3 and PRI-J4 are "outputs" which can be connected to a cascaded backplane, which I don't have.

The manual further says that PRI-Jn are SFF-8643 connectors, which can transport the signals for 4 SAS or SATA drives. That means that I can use 8 HDDs with the backplane, although it mechanically provides 12 drive connectors.

What do I need to do to use 12 HDDs with that backplane?

Please forgive me if the question is dumb, but I have no experience with backplanes yet, and I have studied this and other Supermicro manuals several times, but still don't understand the situation.

Update / Clarification

I am very sorry that I have not been clear enough:

I'd like to use SATA drives (not SAS), and I already have a LSI 9361-8i connected to the backplane, using two cables with SFF-8643 connectors at each end. That way the controller is seeing 8 drives. Now I'd like to know how I can use the remaining 4 drives.

The board I am using has two SATA / SAS controllers integrated, each of which can handle four drives. Do I just need to connect one of them to PRI-J3 of the backplane?

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  • Huh? All you need to do is plug it in. Connect ONE cable from your HBA to PRI-J1. Is your HBA not seeing all 12 drives? What model is it?
    – Michael Hampton
    Aug 23, 2020 at 19:24
  • I am very sorry that I have not been clear enough. I'd like to use SATA drives (not SAS), and I already have a LSI 9361-8i connected to the backplane, using two cables with SFF-8643 connectors at each end. That way the controller is seeing 8 drives. Now I'd like to know how I can use the remaining 4 drives. I'll update my question accordingly.
    – Binarus
    Aug 23, 2020 at 21:39
  • Off topic. Questions on Server Fault must be about managing information technology systems in a business environment. Home and end-user computing questions may be asked on Super User, and questions about development, testing and development tools may be asked on Stack Overflow. While this is pro equipment, the user is asking basically for reading the manual by now, and this is not handled here.
    – TomTom
    Aug 23, 2020 at 21:53
  • I am not asking for reading the manual. I have read the manual multiple times, and other manuals, even from different manufacturers, as well, in the hope to gain an understanding of the situation. However, I failed to do so. Furthermore, I first have asked that question on SU, but it has been migrated here.
    – Binarus
    Aug 23, 2020 at 21:56
  • You are. YOu lack totally basic understanding how SAS works at all. We do not teach these basics here.
    – TomTom
    Aug 23, 2020 at 21:56

2 Answers 2

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What do I need to do to use 12 HDDs with that backplane?

You connect ONE SAS CABLE from your HBA to the backplane. DONE.

There is nothing more. THe backplane is handling the distribution of hard disc signals. SAS is like a storage network protocol and the backplane is like a switch - with every port to one HDD and the outputs for chaining for the next backplane.

Updating for the updated question:

I'd like to use SATA drives (not SAS), and I already have a LSI 9361-8i connected to the backplane, using two cables with SFF-8643 connectors at each end. That way the controller is seeing 8 drives. Now I'd like to know how I can use the remaining 4 drives.

The solution to that is to LEARN THE TECHNOLOGY. You ahve serious misconecptions. There is no two cables for SATA.

Let's start:

  • You can use SATA discs in a SAS backplane. SAS implements a SATA passthrough protocol so SATA discs show up.

  • The 2 cables are NOT for 4 discs each. RTFM. SAS is a network protocol. For uptime and more bandwidth, SAS discs support 2 uplink connections. Hence two cables. This is EVERY DISCS IS CONNECTED TO BOTH CABLES AT THE SAME TIME.

  • SATA discs are not. THey only support one uplink. So, RTFM aside which may decide to split that, IIRC, all discs connect to ONE CABLE. You can literally have hundreds of discs on one SAS link. When you use SATA, all connect to ONE of the two cables, in most backplanes that is link 1. Link 2 is not used then as NONE OF THE DISCS CONNECT TO IT.

So, the whole "4 one one, 4 on the other" is a clear sign of lacking ANY manual reading for SAS, sorry. There is no "4 discs". A SAS link is equal to 4 SATA links in bandwidth, but it still runs a combined network protocol that the backplane handles. Grab an introductory book on how SAS works. If the last 4 drives do not show up, this has NO correlation to the cabling - it is either a bad connection on the discs, a defective board, bad jumper settings somewhere OR - bad power cable connectivity. THere are a LOT of power inputs in a SAS board because of the limits of every MOLEX connector, so discs are grouped with separate power supplies provided. If everythign works as perfect, ONE cable (all that is needed) will provide connectivity for hundreds of discs. Again, this is a NETWORK protocol.

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  • Thanks and +1. However, I haven't been clear enough, and I apologize for that. I'd like to use SATA drives (not SAS), and I already have an LSI 9361-8i connected to the backplane, using PRI-J1 and PRI-J2 (two cables, each handling 4 drives - the controller sees 8 drives). Now I'd like to know how to use the remaining 4 drives (via another HBA or mainboard-integrated controller). Please see the update / clarification in my question.
    – Binarus
    Aug 23, 2020 at 21:50
  • "I'd like to use SATA drives" DO IT - SAS implements SATA passthrough as protocol and it should just work. And with SATA drives there is no "two cables, each handling 4 drives" - SAS uses 2 cables because SAS discs can handle being connected to 2 SAS connections AT THE SAME TIME. SATA does not. ALL sata discs connect to the first cable, the second goes unused. I suggest STRONGLY to start learning the technologies you use, or hire an admin. THis is going from "bad" to "really no idea how things work" and we do not teach basics here.
    – TomTom
    Aug 23, 2020 at 21:52
  • Thanks again. So you answered my question, which I will of course accept. By the way, I am quite experienced with assembling PCs, but this backplane thing is totally new to me. I tried hard to understand it myself, but was mislead by the fact that there are many cables from SFF-8643 to 4xSATA, so I thought that one cable was handling 4 drives.
    – Binarus
    Aug 23, 2020 at 22:00
  • Well , noone says you have ZERO skills - you can be a star rated cook, it is irrelevant, you lack any knowledge about SAS at all. The breakout cable is used for exactly that - breakout. So you can use hat to drive cheap SATA drives without backplane. Note the "without". You may be someone putting parts together, but you need to learn the basics about SAS.
    – TomTom
    Aug 23, 2020 at 22:01
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If you have the -EL1 backplane, you should be able to see all 12 drives, even with a single cable from the RAID card to the expander backplane. If you don't, something's wrong with the backplane or the drives, as the previous answer states.

To clarify some of the other subquestions:

  • A single cable carries 4 12Gbps SAS lanes. If connected to a passive backplane without an expander, it can only be used for 4 drives. With an expander though, it just provides bandwidth between the RAID card and the expander, and the number of drives that can be used depends on how many ports are attached to the expander (including both the directly attached drives as well as any downstream backplanes attached via the cascading ports). There will be limits on the total number of drives, but they're usually large enough (eg 128+) to not matter.
  • The -EL1 backplane has 2 "upstream" connections not for dual-port SAS, but to provide higher bandwidth to the RAID card. For HDDs this won't really matter, it might matter if you install SSDs in all the drive bays. The -EL2 backplane has two expanders and supports dual-port SAS drives, as well as dual RAID controllers, for high availability.
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  • Thanks for the explanation, and +1.
    – Binarus
    Aug 5, 2023 at 9:23

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