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Which host FC is attached to which Array FC? (VA7400)

William Wan_1
Frequent Advisor

Which host FC is attached to which Array FC? (VA7400)

Hi,

We have a VA7400 with 2 FC controller and there are 2 Redundancy Group.
I understand that each Group has it's own primary controller. But how can I determinate which RG is using which controller?

And how to determinate which HOST FC controller is attached ( through a separated SAN switch ) to which controller on the ARRAY?

I need this information to set up a good VG using the most direct PATH to a PV.

Thanks in advance !

William

PS: I attached a output of armdsp -a
5 REPLIES
Uwe Zessin
Honored Contributor

Re: Which host FC is attached to which Array FC? (VA7400)

If I recall correctly, it is a fixed relationship: RG1 is managed by controller 1, RG2 by the other one unless one of the controllers fails.
.
Bernhard Mueller
Honored Contributor

Re: Which host FC is attached to which Array FC? (VA7400)

William,

Uwe is right, C1 is primary for RG1 and C2 is primary for LUNs in RG2.

you do not mention which hosts/OS and FC switches you have, though I would assume HP-UX and Brocades; so ...
- armdsp shows you the WWNs for the VA controllers

login to the switches
- switchshow shows you the ports and the WWNs connected

login to the hosts and (depending on your card)
- ioscan -fnkCfc
shows your FC cards and devices
either of
-fcmsutil /dev/td#
-fcdutil /dev/fcd#
shows you the WWNs

make a drawing of your SAN and make sure that your *primary* paths to any PV of your VGs *always* go through the primary controller for the respective LUN.

Regards,
Bernhard

William Wan_1
Frequent Advisor

Re: Which host FC is attached to which Array FC? (VA7400)

Great answer, thanks,

Yes, it's HP11.0 with brocade switches.

What happend if I use the "wrong" path?

Say, there is a LUN 1 from RG 1 is using VA cntl 1 attached to switch 1 to FC card td1
PV c1t0d1 is using LUN 1 and td1
PV c3t0d1 is using LUN 1 and td2

If a VG is using PV c3t0d1 as primary path, what are the consequences? some read/write command latency?? higher queue on disk subsys??
Bill Costigan
Honored Contributor

Re: Which host FC is attached to which Array FC? (VA7400)

Access will be a little slower. The controllers are connected internally. If the wrong controller gets a read or write for a LUN belonging to the other, it passes the request and receives the data from the other controller and returns it to the system.

According an HP performance paper the difference is minor.
Bernhard Mueller
Honored Contributor

Re: Which host FC is attached to which Array FC? (VA7400)

William,

well.... what Bill says is the official answer and widespread opinion. However, I do know of a case where there was a problem in shutting down a database in time. And believe me or not, all that was changed was this primary/alternate path setup going to the wrong controller. And from then on it worked like a treat.

That is the reason why I *strongly* recommend to always make sure your link is with the primary VA controller.

Regards,
Bernhard