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MSA2312sa Cabling Question

SMaximus7
Occasional Contributor

MSA2312sa Cabling Question

I have 4 clients connected to an Dual Controller MSA2312sa.  I was using the following as a cabling method (just seemed logical to me)...

Server 1 - A1 and B1

Server 2 - A2 and B2

Server 3 - A3 and B3

Server 4 - A4 and B4.

 

HP is saying we should use the following method

Server 1 - A1 and B1

Server 2 - A2 and B2

Server 3 - A3 and B4

Server 4 - A4 and B3

 

Can someone tell me why server 3 and 4 have to mismatch?  I'm trying to understand why that would matter.  Thanks

 

 

 

4 REPLIES
Johan Guldmyr
Honored Contributor

Re: MSA2312sa Cabling Question

"HP is saying" - are they referring to some kind of best practices document? There may be some of those around.

If HP says you should cable it that way, why not ask them for the reasoning.

 

Maybe this is something physical - perhaps it's in some cases easier or you can use a shorter cable if you cable it like this.

 

It sounds a bit odd that S3 and S4 only should mismatch - it might make it a bit harder to troubleshoot.

Maybe it's just a typo?

Anyway, from a fault-tolerance perspective it seems better to connect to both controllers (because then you can survive if one controller goes down). But from a performance perspective, it may be better to connect one server to one controller (because only one controller has vdisk ownership).

SMaximus7
Occasional Contributor

Re: MSA2312sa Cabling Question

Hey Johan.  I got that information from this HP cabling guide http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c01755933/c01755933.pdf.  

 

I also think its ridiculous to have only those two mismatch and think it was some sort of typo on their end.  I have contacted HP about this and their support knows as much about it as I do (conforting). 

 

As far as the fault-tolerance vs performance.  You can still plug them into both controllers and then just choose the vdisk owner in the SMU.

 

I'm currently getting some device\RaidPort reset and drops (no data drops but I do get events logged on the server and MSA).  I called them to troubleshoot and they had me make sure my cabling was set according to their supported configuration, but they can't give me a rhyme or reason why the last two ports have to be configured that way.  Now I have to go and reconfigure those two cables on a highly important Production environment.  I don't like making changes to my Production environment without first understanding why I'm making the changes and this changes just seems ridiculous to me. 

 

Maybe one of their techs will come accross this post and will be able to shed some light on this for us.

Johan Guldmyr
Honored Contributor

Re: MSA2312sa Cabling Question

Ah, nice document. Too bad it's not possible to read which port is A1 or B2 :)

Are the two top ones port 1 and 2?

"As far as the fault-tolerance vs performance. You can still plug them into both controllers and then just choose the vdisk owner in the SMU."

Is it possible to on your server prioritize the path that goes to the owning controller? With FC you can but haven't used the SAS versions.

If the tech that has your case cannot answer it, why not ask if they perhaps could ask for some help from the next level?
SMaximus7
Occasional Contributor

Re: MSA2312sa Cabling Question

Top two are 3 and 4, bottom are 1 and 2.

 

With SAS there isn't much you can do on the server end.  You can prioritize the path in the SMU only, by choosing a vdisk owner, so, if you choose controller A, whichever cable is connected to controller A is the primary path.  If that path should fail it will failover to controller B.

 

I've even reached out to my HP Storage Speciallist and didn't get far there either.