Multi Paths and Emulex HBA's

[John Hooper_1]

Gday Everyone,
Just hoping someone might have Emulex HBA's in operation here. I have a mixture of Emulex Lp9002L,Lp8000,Lp850 HBA's in operation. I am using IP over fibrechannel with there specialised drivers as well. All hooked up via a brocade switch. I have a HP VA7400 with 60 disks. This unit has 2 controllers. I have a mixture of Windows2000 and WinNT Servers. I only have 1 HBA in each Server and not using HP Autopath. At the moment I have 1 controller zoned off on the Brocade so I dont end up with double disk entries due to multi paths to the same LUN. I just want to find out if there is any other cost effective way other then Autopath that I could ebable that second controller and the be able to have redundant paths. I noticed in the Emulex HBA drivers there was a option to 'Enable Multiple Paths To SCSI Disk' From the little bit of reading I have done this option is for muiltiple HBA's in the server (Or I may be wrong) Any information would be great. Thanks for all you help.

Johh

[Vincent Fleming]

Unless you have a fully redundant environment (2 HBAs per server, 2 switches, 2 controllers), there isn't much point in having redundant paths to the array, as it will not significantly increase your availability.

I am unaware of any software available for Windows that will do what you want with your configuration.

The idea of the redundant paths is to eliminate any SPOF (Single Point Of Failure) within the connection between the host and disk array. Without multiple HBAs and multiple switches, you still have 2 SPOFs (the HBA and the switch).

Good luck!

[John Hooper_1]

G'Day again,
Is there any performance problems with having both redundancy groups running from the single controller ? If Controller 1 looks after Redundancy Group 1 and Controller 2 looks after Reduundancy Group 2 and You only have Controller 1 plugged in making Redundancy Group 2 continually failing over to Controller 1, there would be a performance problem ? In that case all the Servers using LUN's on Redundancy Group 1 would have better performance then the ones with LUNS's on Redundancy Group 2. Would switching the Array settings to Single Controller Mode help with this in any way ? Any input would be appricaited. Thanks,

John

[Vincent Fleming]

When using a single path to the array, the controller that receives the I/O will forward any I/Os for non-local RGs to the other controller.

For example, you're using controller 1 only. An I/O to a LUN on RG2 would be forwarded to controller 2 for processing. The data would be returned by controller 1.

There's an 800MB/s bus between the controllers.

You are correct assuming there is a performance penalty for this... The time it takes to forward the I/O will degrade your performance by increasing your latency on RG2 LUNs.

I don't know exactly what single controller mode does (I haven't seen a technical description of that mode of operation), so I don't know if it would help your performance. Try it, and let us know if the performance picks up at all.

Come to think of it, if you were to put the unit into single controller mode, and remove the unused controller, it would process all I/Os from the single controller... which may increase your performance because it's not forwarding the I/Os for RG2 to controller 2.

Hmm... You could also zone your switch into 2 basic zones... one for controller 1 and one for controller 2. Hosts in the controller 1 zone could be assigned LUNs from RG1 only, and Hosts in the controller 2 zone could be assigned LUNs from RG2 only; This would make sure that you use both controllers and that all I/Os are processed by the controllers locally, giving the best performance possible.

Good luck!