multiple alternate links

[Unix Administrator_5]

I have an hpux 11.0 k580 running advanced jfs and mirror/ux.

We currently have volume groups that have a primary path and an alternate link.

Due to some configuration changes we are going to have a primary link and three alternate paths.

Will hpux and software support these alternate paths, and how does it go through and decide which alternate to use.

[Pete Randall]

Yes, HP-UX will support multiple alternate links and it will use the primary.

Pete

[David Bell_1 · Accepted solution]

Yes it will support multiple alternate paths. It will give the first assignment based upon primary controller configuration. By this I mean that if you have controller '1' and controller '2' and the LUN is created with controller '1', '1' will be primary and '2' will be alternate. If you're doing this through a SAN/switch, it will use the sequential numbers next in line to be alternate '2' and alternate '3'. These can be manipulated by using vgreduce/vgextend. You would vgreduce the 'primary' link from the VG. The first alternate would then become primary. You can then vgextend the 'old' primary back as an alternate. Use this to balance the load across the controllers, HBA's, and ports.

HTH,

Dave

[S.K. Chan]

As far I know the choice of which alternate path it chooses depends on the order it appears in your "vgdisplay" output. For example =>
--Physical Volumes---
PV Name /dev/dsk/c0t0d0
PV Name /dev/dsk/c7t0d0 Alternate Link
PV Name ......
PV Name ......
in that order that you see.

[James R. Ferguson]

Hi:

LVM utilizes the primary link only. No load-balancing with an alternate(s) occurs. Secondary (or tertiary) links exist only for fail-over. The primary link is nothing more than the first physical path to a device as defined in '/etc/lvmtab'.

To exchange a primary for a secondary link, 'vgreduce' the primary and 'vgextend' the *same* link back into the volume group.

While LVM does not load balance, you can and should allocate multiple links to different controllers. In this fashion a group or array of disks can be serviced by multiple controllers (paths) thereby improving throughput. To a particular disk, only one pv-link is active as indicated.

Regards!

...JRF...

[Bugs_Bnny]

Hi All ,

We can also use "pvchange" to switch the primary and alternate paths online ..no need to vgreduce and vgextend

Enjoy,
Rajesh