Primary/alternate links, VA7400 and LVM

[Murat SULUHAN]

Hi

I am using VA7400 with 2 HP-UX servers and 2 Brocade. My question is about LUNs and primary/alternate links for VGs.

I successfully created a LUN in redundancy group 1 and when I want to create a new VG or extend previously created VG on the disk-array with this LUN, how can I determine which device is primary link and which is secondary link

Best Regards
Murat

[Bernhard Mueller]

Murat
vgdisplay -v will tell you

if you need to reverse:
vgreduce
vgextend

(LVM automatically makes the alternate link the primary after the vgreduce, so vgextend with the same device will make that device the alternate link)

Regards,
Bernhard

[Murat SULUHAN]

Hi Bernhard

I already know this command, but HP configured our initial VGs,

I attached a file about ioscan -funC disk and vgdisplay -v outputs from same host.

For example vg01 has 4 LUN and first 2 LUN's primary link different from others. I cannot figured out. and vg02 also has 4 LUN and all of them has belong to same primary link.

So I want to learn how to configure array but I don't understand primary links and LUNs with these situation

Thanks for your response,

Best Regards
Murat

[Jim Viera · Accepted solution]

Murat,

I assume that you have 2 separate SAN fAbrics. The host hba that's attached to the fabric with controller 1 of your VA7400 should be your primary path for the LUNs you create in redundancy group 1. The opposite is true for the LUNs you create in redundancy group 2.

We have 2 SAN fabrics with two VA7400's but we are NOT using the same Domain ID's on both fabrics.

You will need to match your host hba's with the VA7400 hba's and assign primary and secondary accordingly.

Regards,
Jim

[Bernhard Mueller]

Murat,

LVM uses the alternate link for data transfer only if the primary link fails.

You have two HBAs and so for each LUN you have two path.

In order to setup a static load balancing using *both* paths you would usually alternate the primary link either for each LUN or with each VG

This has not been done consistently. If I were you I would use vgreduce/vgextend and make the /dev/dsk/c5 device files the primary link for all even LUNs (d0, d2, d4, d6) and the /dev/dsk/c7 device files the primary link for all odd LUNs (d1, d3, d5, d7).

As long as ioscan -fnCdisk shows all devices claimed you can do this without risk and on the fly.

Regards,
Bernhard