supermicro chassis SC846, backplane questions

[nephri]

Hi all,

I'm currently under discussion with a seller for buying 2 chassis made like this:
- Chassis : SC846E1-R900B
- PSU : 2x 900W PWS-920-1R
- BackPlane : BPN-SAS2-846EL1 (replace the original SAS1)

I would change the PSU with a SQ model, but it's not the purpose of this post.

I readed the BPN-SAS2-846EL1 documentation because i want to be sure that this backplane will not be the component responsible of any throughput limitation in the final build.

So, i'm not really familiar with backplane and expanders and i saw it has 3 primary connectors called PRI_J0, PRI_J1, PRI_J2 but i don't really found any documentation of how theses connectors works and can be used.

I would know if i can connect 3 HBA to the backplane ? Or connect a single HBA to the backplane using 2 or 3 connectors ?

I understand that i can't use failover because the EL1 don't have a second expander chip. But this not a mandatory feature and since i will probably use SATA drive (enterprise class), it's not an issue.

So, finally i don't found what is possible to do and what is not with HBA <---> BPN-SAS2-846EL1 .
I would have your welcome advices on which architecture i should do for have a 24x hard drives with the maximum throughput.

I have to say that i have plan to use a dual 10 Gb NIC using SFP+ connector (i just bought a Gnodal GS4008 switch). But if all goes well i will maybe able to use a single 40 Gb NIC using QSFP.

I want to build this server for NAS / SAN purpose over FreeNas (or at least a vanilla FreeBsd)


- Which HBA i should use (only one or more than ones ) ?
- Which cables i should use (it seems to be the SFF-8087 from documentation i saw) ?
- How many cables ?

The SFF-8087 seems to be a 4x SAS channels at 6Gbs/s = 24 Gbs/s.
It would be sufficient for a dual 10Gb/s NIC but not for a single 40Gb/s NIC if i use only one cable.

I would also know if it has a real advantage to go with a SAS3 backplane (12 Gb/s) ?
With SATA drive at 7200 RPM, it doesn't seem to be an high plus-value, have missing something ?
With SSD it should be significantly different.

I do this post because i don't want make a mistake with this buy because it represent a significant cost and i want to be sure where i go. Maybe i'm having wrong questions...

Thanks in advance for your helps.
Best Regards,
Sébastien.

PS: sorry for my poor english, i'm french.. (i know it's not an excuse )
I posted the same message in FreeNas forum.

 

[halfelite]

If my memory is correct the BPN-SAS2-846EL1 only supports a single path the BPN-SAS2-846EL2 supports multi path.

But I think I also remember something along the lines the BPN-SAS2-846EL1 will support two cables from one card un-officially

But people around here have way more knowledge then me on it so wait for someone else to chime in.

 

[nephri]

Thanks for your reply,

You point exactly questions i have ! And i want to be sure before to click on "Buy" :-/

In all cases, if the chassis is filled with 24x SATA drive at 7200RPM and considering each drive can have an average transfert about 80 Mo/s
We will go to 1.8 Go/s througtput (if all disks are actives). This is below than the SFF-8087 can wire around 2.4 Go/s (if i'm right).

But with an average speed of 120 Mo/s, the backplane could be in this case a limitation.

In real use, do you think a single path using a SFF-8087 cable over 24 SATA HDD could be a throughput issue ?

Best regards,
Sébastien.

 

[xnoodle]

The two cables from one card feature is called dual link. You can dual link your HBA to the SAS expander, and connect the third port to a rear external SAS connector.

 

[nephri]

This backplane supports the dual link ?

Wich hba you would recommand ?

 

[xnoodle]

Yup, that backplane should. It uses the LSI 2x36 chip IIRC, so there are 36 "ports", 24 that go to the backplane, 12 that go to the 3 SFF-8087 ports.

I would recommend a LSI based HBA. See https://forums.servethehome.com/ind...and-hba-complete-listing-plus-oem-models.599/ for a nice list

I'm not sure what the current choice is for a cheap LSI card. In the past, the IBM M1015 (LSI 2008 based) was the de-facto cheap one to get. There were deals earlier this month for cheap Dell H310. Also depends on where you are physically located.

 

[PnoT]

What's the point of hooking up 2 cables anyway on a backplane that has just one expander?

 

[nephri]

The idea is to have more than 4 lanes to the HBA but 8 in order to not be bandwidth limited.
Is it a bad idea ?

 

[PnoT]

The idea is to have more than 4 lanes to the HBA but 8 in order to not be bandwidth limited.
Is it a bad idea ?

Is that true and if so which ports do you connect because the manual states the one port for connectivity with the other two for other duties. I'm curious as I only have one cable hooked up right now and would like some background info on this type of setup. Good topic!

 

[nephri]

Effectively, i didn't found any documentation regarding the "dual linking" for the BPN-SAS2-EL1
This topic is done for determine if it's possible or not.
I think SAS2 is enougth since an HDD can't saturate a 6Gb/s lane alone (except for SSD).

But if the expander can only handle 4 lanes (6*4 Gbs), 24 HDD can saturate the 4 ports of the HBA.
It's why, i want to be sure than i can connect 8 ports to the HBA instead of 4

If anyone had already do such things, feedback are welcomes.

 

[PnoT]

Any info on whether this is possible and to which ports on the backplane need to be connected?

 

[nephri]

From FreeNas forum, someone have tried it without complete sucessfull.
He seems to have less performance with 8x "port wire" compared to the 4x.
It seems to be not trivial as it seems.

 

[nephri]

I emailed supermicro for having informations about dual linking

BPN-SAS2-EL1 : 1 chip, just 4 lanes, no dual linking at all
BPN-SAS2-EL2 : 2 chips, 8 lanes but only for failover (with SAS drives only). So no dual linking at all
BPN-SAS2-846EL2 : 2 chips, 8 lanes supporting dual linking. The chassis reference provided by SM is 846BE26-R1K28B

I'm always in discussion with supermicro for more informations. I will give you feedback.

PS: The commercial/tech support of SuperMicro (EU one) give answers very fast. I'm really impressed !!! It's relatively rare with such companies to notice.

Best regards,

 

[nephri]

Oups, a reply back from SuperMicro

They answer a mistake, BPN-SAS2-846EL2 supports only failover dual linking but none for efficiency.
They have no backplane for dual link aggregation.

So no plan to achieve that... it's a bad sound for me...

 

[PnoT]

Thank you for taking the time to dig into this question as I had always wondered myself.

 

[sth]

Curious....can I replace any 846 chassis backplane with a BPN-SAS2-846EL2? I have a pair of 9211-8i's which could support failover I believe.

 

[BlueFox]

Backplanes are a bit of a pain to swap, but they're generally interchangeable. Compatible with the 847 series too (well, the front). I've owned the A, TQ, and EL versions and they appear to be identical to mount.

 

[T_Minus]

Well that sucks.

I was hoping they were dual-port for my ZeusRAM drives... how is one supposed to fully utilize these if the backplanes don't support it?

 

[nephri]

you can use a BPN-SAS-846A that has no expander chip, you have to connect 6 SFF-8087 connectors (so it means 3 height ports SAS HBA)

 

[ponky]

I have a SC846 (SC846BA-R920B to be exact). I've replaced the TQ backplane (no expander) with BPN-SAS3-846EL1 SAS3 backplane with expander. It was not hard to replace, took maybe 10 minutes total.