HPUX 11i Multi-Path

[Matthew S. Luth]

I need some clarification about multi-path. Is there inherent multi-path failover support in HPUX without the addition of special drivers?

I found a reference in the 10.30 release notes to being able to assign the "primary" path to devices in LVM. That seemed to imply that the path failover was inherently available.

Does HP AutoPath simply add the I/O load balancing on top or is it required for automatic path failover also?

Please enlighten me.

Thanks,
Matt

[Sridhar Bhaskarla]

HI Matt,

No. The failover path is not available until you add it. For ex., c0t1d0 and c1t0d0 are two links to the disk, then in order to get the alternate link configured, you will need to vgextend the other disk.

#vgcreate (options) vg01 /dev/dsk/c0t1d0
#vgextend vg01 /dev/dsk/c1t0d0
#vgdisplay -v vg01
(this will show c1t0d0 as the alternate link)

In case of failures, LVM will automatically switch the primary path to the secondary and will switch back after a recovery.

For load balancing and more discussion on alternate links, look at the following recent threads.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xb10c31ec5e34d711abdc0090277a778c,00.html

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xdf0a31ec5e34d711abdc0090277a778c,00.html

-Sri

[Sridhar Bhaskarla]

A small correction. Replace the example link c1t0d0 with c1t0d0.

-Sri

[Vincent Fleming · Accepted solution]

Matt,

I think Sridhar slightly misunderstood your question...


Yes HP-UX comes with path failover capability built-in to LVM. It's called PV-Links. Sridhar is correct in that PV-Links does not become active automatically - you need to configure LVM to use it.

But it's there.

Anyway, AutoPath or SecurePath (depending on your disk array model) adds load balancing in addition to path failover. (they do not use PV-Links, but are independent implementations)

I hope this helps,

Good luck,

Vince

[Vermeulen Peter]

Secure Path seems to me the best option but it is quite expensive, that's why we are just using the standard PV-links for alternate pathing.
This means we don't have any automatic load balancing right now.
However we tried to use a different path to our array for the first link. This means that for 2 different volumes we got 2 different paths as the first link.

[Sridhar Bhaskarla]

Hi Matt,

AutoPath is specially designed for true loadbalancing and fault-tolerance. So, it is much superior to the built-in LVM alternate link feature.

Autopath does do both independently of LVM. Depending on your setup, you can even use LVM to loadbalance but it means extra configuration. And balances better if you do lvm striping.

So, if you want true load balancing you may want to consider Autopath.

-Sri

[Sridhar Bhaskarla]

Hi Matt,

Auto|SecurePath, an additional software is specially designed for true loadbalancing and fault-tolerance. So, it is much superior to the built-in LVM alternate link feature. It does do both independently of LVM.

Depending on your setup, you can even use LVM to loadbalance but it means extra configuration. And balances better if you do lvm striping.

So, if you want true load balancing and fault tolerance with minimum effort you may want to consider Autopath. It it costs you $$.

-Sri

PS: I was to add comments about Autopath in my previous message but forgot.

[Sridhar Bhaskarla]

Hmmm.. Didn't not realize that I clicked submit while I was writing the message. I apologize for the making this thread a mess.

-Sri