BPN-SAS2-826EL backplane question

[Herdo]

I just ordered a Supermicro CSE-826 case (12-bay) which comes with a BPN-SAS2-826EL backplane.

 

I'm starting to question my decision because after looking at some pictures of the backplane, there appears to be only 2 SAS connectors.

 

https://www.thomas-krenn.com/de/wikiDE/images/7/76/Backplane-BPN-SAS2-826EL1-back.jpg

 

How does this work?  Shouldn't there be 3?  I was under the impression that 1 8087 connector handled 4 drives, but maybe that isn't right?  I'm questioning how I am going to connect 12 drives to this thing.

 

Maybe it will just lower the throughput of the drives if they all run off of two?

 

Also, this page https://www.thomas-krenn.com/en/wiki/BPN-SAS2-826EL1_SAS_Expander_Backplane is stating that:

 

"All drive slots are connected by a single cable with the RAID controller"

 

Now I'm more confused than ever. 

 

I did however find an old ebay listing selling the BPN-SAS2-826EL1 and it says in the description "3 sas ports", but the funny thing is that their picture only showed 2 ports as well.  So maybe I'm just not seeing the third port somewhere?

 

Can someone help me out here?

 

 

 

EDIT:  After talking to somebody else on Reddit, it appears I was right about it working with all 12 drives but limiting bandwidth, and all 12 drives connect through just 1 SAS connection.  Considering there is no striping with unRAID and I'm connecting through a 1Gbps NIC, I shouldn't hit any sort of bottleneck with this backplane though.

 

I guess my only question now is, will this still work with an H310 flashed to IT?  It has 2 sas connectors, but the description says "8 ports".  Will that matter, or should it still work fine with all 12 drives through 1 SAS connection?

[JorgeB]

The BPN-SAS2-826EL has a built-in expander, there are 2 models, the one you linked is the BPN-SAS2-826EL1 with a single link expander, there is also the BPN-SAS2-826EL2 with a dual link expander.

 

It *should* work with a flashed H310, use only one link, the other SAS connection is for cascading with another backplane.

 

Single link bandwidth is just enough for 12 disks, even during parity checks/syncs, the max will be ~185MB/s, as long as the expander is SATA3 compatible (and it should be), and all your disks are SATA3, avoid mixing older SATA2 HDDs or it will bring the whole speed down.

[Herdo]

Hey, thanks for the reply.

 

The BPN-SAS2-826EL has a built-in expander, there are 2 models, the one you linked is the BPN-SAS2-826EL1 with a single link expander, there is also the BPN-SAS2-826EL2 with a dual link expander.

 

It *should* work with a flashed H310, use only one link, the other SAS connection is for cascading with another backplane.

 

That's basically what I have found.  It's got two ports but the second is used for connecting to another backplane.

 

Single link bandwidth is just enough for 12 disks, even during parity checks/syncs, the max will be ~185MB/s, as long as the expander is SATA3 compatible (and it should be), and all your disks are SATA3, avoid mixing older SATA2 HDDs or it will bring the whole speed down.

 

I actually figured something different.  If it's a SAS 2 port, wouldn't that be 6Gbps?

 

6Gb/s = 6000Mb/s

 

6000 / 8 = 750MB/s

 

750 / 12 drives = 62.5MB/s

 

Or am I not understanding how this works?

 

Thanks again!

[JorgeB]

A 4port SAS2 link has 2400MB/s (4x 600MB/s) max theoretical bandwidth, in my tests I've found real world speed is ~2200MB/s, so:

 

2200 / 12 = 185MB/s

[Herdo]

A 4port SAS2 link has 2400MB/s (4x 600MB/s) max theoretical bandwidth, in my tests I've found real world speed is ~2200MB/s, so:

 

2200 / 12 = 185MB/s

 

Oh OK, thank you.