High Availability and Alternate links

[Omar Alvi_1]

Hi,

When I create a volume group, I get an error message stating that vgextend failed because of an IO error and the alternate link could not be added. The vg can still be created but there will be no alternate links.

There are many issues hidden in this scenario which I would request clarification for

The hardware setup is two rp3340s, a NAS MSA 1000, two fiber channel switches, and four fibre cables. Now we've been told that the MSA 1000 doesn't support 2 controllers, so we've got no physical alternative links. One fiber cable from either system to the single switch interfacing with the MSA.

Is such a configuration where there's no alternative links supported for serviceguard?
How does thae system percieve that there should be alternative links?
What should be the way forward?

I hope I've been clear.

Appreciate any assistance.

Thanks and Regards,

-Alvi

[melvyn burnard]

If this is a NAS device, it is not supported in Serviceguard as shared storage.

[Stephen Doud]

As Melvyn stated, Serviceguard works with Fibre-channel Mass Storage connectivity (SAN) - not LAN-based connectivity (NAS).

If the MSA 1000 is SAN-attached, then dual-pathed LUNs in the array would be discovered (ioscan, insf -e) and presented as two different /dev/dsk/c_t_d_ special files.
The Admin may forget to vgextend one path into /etc/lvmtab, but a vgimport using a map file with the VGID at the top will cause LVM to discover both paths to the LUN and report the discrepancy (albeit is NOT a showstopper for supported versions of Serviceguard)

[Dave Wherry]

The MSA is not a NAS device. It is a SAN device. While it does have 2 controllers they run Active/Passive.
So you were correct that the host would not be able to see the LUN on the alternate path.
I'll tell you I've never thought about how to configure the alternate link. You might be able to create the logical volumes and then fail the active controller on the MSA. It might crash your system when you lose the whole volume group. If not, when the second controller takes over you should see the LUNs and might be able to add the alternate links. Of course at that point, what was your primary links are not available on the first controller.
It's all kind of sloppy. This is probably one of the reasons why HP still does not strongly recommend the MSA for HP-UX systems. The MSA is supposed to become Active/Active this year. At that point it will be a better option.