SAS Controller & Expander Questions

[iolaus]

I recently purchased a AIC RSC-4EG2 chassis which came with what I believe are 2 BKP-SAS3-12EG-R backplanes. Each of these backplanes has 3 SAS connectors, two of which are labeled as "uplink" and one of which is labeled as "downlink". From this SAS expander white paper I found it seems "uplink" refers to a connection between the HBA and the expander while "downlink" refers to a connection between the expander and some external storage.

With that in mind, what is the optimal way for me to connect my two backplanes? Is it best to have two dual port HBAs (perhaps M1015s) each of which has one port connected to each backplane? Will I see any bandwidth increase by utilizing both "uplink" ports on each backplane or is it simply for redundancy?

Finally, is there an easy way to determine what type of SAS connector the backplane uses?

 

[Dalfo002]

The high density (uplink) connections on your backplanes are likely to be SFF-8087

I would tend to think the dual uplink ports on the backplanes (assuming that they are indeed SAS expanders) would be for redundancy, but that would be little more than a guess and I cannot answer any of your other questions with any authority.

be certain that the backplanes in your case are indeed expanders and not simply forward breakout backplanes (meaning, did you find the whitesheet based off a part number or just one that looked about right). The fact that you have 3 SFF-8087 (4 lanes each) and 12 drive ports suggests that a simple breakout backplane exists for that case in addition to the expander version you pointed to.

 

[iolaus]

Be certain that the backplanes in your case are indeed expanders and not simply forward breakout backplanes (meaning, did you find the whitesheet based off a part number or just one that looked about right). The fact that you have 3 SFF-8087 (4 lanes each) and 12 drive ports suggests that a simple breakout backplane exists for that case in addition to the expander version you pointed to.

Dalfo002,

Thanks so much for the reply. I'm relatively sure the whitepaper is the correct one. I know the chassis is a RSC-4EG2 and according to the parts list there are only 5 available backplanes (only one of which is a 12-in-1). Additionally, the diagram in the white paper appears to be identical to chassis backplane down to the individual components and connector locations.

With that said, is there any way to verify that the backplane is indeed an expander? Also, is there any way to verify whether the two uplink ports are for redundancy? I suppose I could always try to contact AIC and see if they're able to provide any additional data.

 

[omniscence]

You should connect both uplink ports to the same SAS HBA. Most expanders will aggregate the links to increase overall bandwidth. However, there seem to be some expanders that have problems with the combined links.

 

[iolaus]

Here are some photos I took as well if this will help anyone with a definitive connector identification or to help me confirm that the backplane is indeed a BKP-SAS3-12EG-R.

Thanks.

 

[Dalfo002]

As stated before, those connections should be SFF-8087

 

[iolaus]

You should connect both uplink ports to the same SAS HBA. Most expanders will aggregate the links to increase overall bandwidth. However, there seem to be some expanders that have problems with the combined links.

Awesome, I just ordered a pair of M1015s so I'll try connecting both ports of each to a single backplane as you suggest. Thanks for the info!

As stated before, those connections should be SFF-8087

Thanks Dalfo002, just wanted to confirm.

 

[D-EJ915]

If you are using SATA drives running 2 cables to the expander/backplane is more than likely pointless. The second connector is 99% likely for the second set of ports on dual-port SAS disks.

 

[omniscence]

There is only one expander chip on the backplane as far as I see. So it is unlikely that the second port is for the secondary SAS ports. I don't see how this would be implemented.

 

[DJ_Datte]

Don't confuse bonding with dualports. The single expander dual ports are just for bonding (doubling of bandwith), for dualport drives, you need two expander chips per backplane, like the E26 versions of any SuperMicro Chassis have (while E16 ones have a single, just like this one).

 

[iolaus]

There is only one expander chip on the backplane as far as I see. So it is unlikely that the second port is for the secondary SAS ports. I don't see how this would be implemented.

Don't confuse bonding with dualports. The single expander dual ports are just for bonding (doubling of bandwith), for dualport drives, you need two expander chips per backplane, like the E26 versions of any SuperMicro Chassis have (while E16 ones have a single, just like this one).

Thanks so much for the info guys. My two M1015s will be coming soon so I should be able to take full advantage of the dual port bonding configuration. Assuming the bonded configuration I would end up with eight 3Gb/s lanes per backplane (or 2Gb/sec/drive) of available bandwidth correct?

 

[patrickdk]

Bonding normally doesn't double throughput, it seems in most cases to give an extra 20-50%
Wonder if it's the hba, or expander doing that.