topic Re: alternate link in Operating System - HP-UX

alternate link

himacs — Sun, 18 Oct 2009 18:21:12 GMT

Hi,

Please find the attached lvlnboot output.How i can avoid the alternate link lines from the output.

and those PVs are used in raw VG.

regards,
himacs

Re: alternate link

Torsten. — Sun, 18 Oct 2009 18:32:57 GMT

You cannot directly, unless you filter the result.

Re: alternate link

himacs — Sun, 18 Oct 2009 18:38:23 GMT

Hi torsten,

Actually why alternate link used,how to create the same.

I didnot get ur answer.

regards
himacs

Re: alternate link

himacs — Sun, 18 Oct 2009 18:46:17 GMT

Hi,

Please find below partial output of vgdisplay

PV Name /dev/dsk/c3t3d0
PV Name /dev/dsk/c5t3d0 Alternate Link
PV Status available
Total PE 3235
Free PE 0
Autoswitch On
Proactive Polling On

PV Name /dev/dsk/c3t3d1
PV Name /dev/dsk/c5t3d1 Alternate Link
PV Status available
Total PE 3235
Free PE 0
Autoswitch On
Proactive Polling On

PV Name /dev/dsk/c3t3d2
PV Name /dev/dsk/c5t3d2 Alternate Link
PV Status available
Total PE 3235
Free PE 0
Autoswitch On
Proactive Polling On

whats alternate link does here..

regards
himacs

Re: alternate link

Michael Steele_2 — Sun, 18 Oct 2009 19:58:04 GMT

Hi

This is the subject of multi path. Native multipathing is pvlinks which is controlled by LVM. EMC Power Path and Hitachi(?) AutoPath are applications other than LVM that perform a similar or superior Mutlti Pathing as LVM and pv links.

MultiPathing is a part of any high availability failover discussion. In this case the primary HBA fails over to the althernate.

Everywhere that you see alternate is the failover HBA device.

Load Balancing is apart of multipathing. Load Balancing prevent's disk bottlenecks. For example, a disk is getting so many read write requests a bottlenect develops. Load balance or the use of both the primary and the alternate instead of just the primary, defeats disk bottlenecks.

Re: alternate link

James R. Ferguson — Sun, 18 Oct 2009 20:35:52 GMT

Hi:

As Torsten noted, if you don't want to see the alternate link output filter it out, ad for example, with 'grep'.

> whats alternate link does here

"Alternate" or "pvlinks" are additional paths to a physical disk. Up to eight alternate links or paths to any one device are supported. The first path as recorded in '/etc/lvmtab' is called the "primary" link and any others (to the same device) are designated "alternate" links. LVM alternate links do not support load-balancing of I/O between the primary and any secondary (alternate) links. Alternate links provide high-availability access only; to allow continued device assess should the primary link fail. In 11.31 a new multi-pathing mechanism know as the mass storage stack, supports native multipathing without using LVM pvlinks.

Regards!

...JRF...

Re: alternate link

Michael Steele_2 — Mon, 19 Oct 2009 01:41:03 GMT

Hi

There is one additional subject that you'll often see re: alternate links, Round Robin algorithm. Note this comment from the above:

"..LVM alternate links do not support load-balancing of I/O between the primary and any secondary (alternate) links..."

The round robin algorithm is a way around this problem. Here is an example:

c1t0d0
c2t0d0
c2t0d1
c1t0d1

-or-

vgcreate /dev/vg01 c1t0d0 c2t0d0
vgcreate /dev/vg02 c2t0d1 c1t0d0

As mention, the first link is the primary. In the round robin procedure, each controller is given a primary link in two vg's.

This is how load balancing is attend in LVM.

But its not very convenient, and applications like Power Path have better drivers to handle load balancing more efficiently.

Re: alternate link

Torsten. — Mon, 19 Oct 2009 04:12:06 GMT

Does your result look different if you run

# lvlnboot -v vg00

instead?