Multipathing/load-balancing across multiple HBA's in Tru64 5.1x

[David Hartman_2]

Is there a way to control multi-pathing & load-balancing among multiple HBA's from within the 5.1x OS? My understanding is that Tru64 will dynamically load balance I/O across multiple paths, but this can cause problems with active/passive arrays. I would like to use the availability feautres akin to PVLINKS without sending I/O down multiple paths (load-balancing) to avoid 'ping-ponging' LUNS between controllers.

Thanks.

[Ivan Ferreira]

Try64 has the multipath support in the kernel, and is a "failover" mode. You cannot activate both controllers, and you cannot control which will be the active controler.

But i don't know why this will be a problem with active/passive arrays, there has been active/passive arrays since the HSZ50. The operating system always tries to use the best available path.

[Devesh Pant_1]

David,

Tru64 5.1x has a pretty good multipathing and load balancing and you should not have any ping-ponging. It will actually provide you a better bandwith and passivity is not to be seen here at all.

thanks
DP

[Mulgund]

Not sure if David want to ask this, But was just curious.
LUN's created using HSG80 controller can have preferred access path set. This LUN detail I guess will not be visible to the OS. Will this not defeat the idea of load balancing?

[Larry Vatkin]

I understand, that David's question focuses not on advantages of MP&DLB, but how to limit it's impact on active/passive arrays, that don't use HSx80 controllers. I've seen similar problems in which those controllers recognized switching of a path as a path failure, which forced them going into diagnostic mode, subsequently slowing down I/O rate.
So, in the absense of a suitable answer, I join David in his question.

[Uwe Zessin]

T64 V5 knows how to tell the difference between an active and a standby path ;-)

You can still cause a failover to a standby path (well, all standby paths on a particular controller) by sendig a 'START UNIT' command down one path with SCU.