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MPIO Load Balance Policy and ALB relationship

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Dave Harrold
Advisor

MPIO Load Balance Policy and ALB relationship

I am trying to understand the relationship between the Load Balance Policy and the Adaptive Load Balancing (ALB) setting. Does the policy have any effect if ALB is off? If yes, what does it do?

This is in reference to the EVA Full Featured DSM for EVA4/6/8 Disk Arrays V3.00.00

Thanks,

Dave
7 REPLIES
Uwe Zessin
Honored Contributor

Re: MPIO Load Balance Policy and ALB relationship

Those EVAs implement A/A/A - Asymmetric/Active/Active presentation. That means that there is still only one controller responsible for maintaining the cache and physical disk I/O for a single virtual disk at a time.
A request through the proxy controller is forwarded to the owning one.

ALB makes sure that requests go only to the paths of the owning controller. It's my understanding that ALB goes first and then the LB policy is applied to these ports.
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Dave Harrold
Advisor

Re: MPIO Load Balance Policy and ALB relationship

Thanks Uwe,

I am familiar with the Active-Optimized and Active-Nonoptimized controller/path behavior.

So, you are saying the LB policy does nothing until ALB is enabled, correct?

Dave
Uwe Zessin
Honored Contributor
Solution

Re: MPIO Load Balance Policy and ALB relationship

No, sorry, that is not what I meant to say.

If ALB is turned off, then LB could go over all EVA controller ports (e.g. when you have selected a round-robin policy).

If ALB is turned on, the LB does not use the ports of the non-owning controller.

--
By the way: there was a documented 'limitation' (I'd call it a bug!) in the V2 MPIO - I don't know if it is still in the V3 (don't have time to test it).

When there was at least one FC port on a server that did not have access to the EVA, ALB did not work at all. I've seen this on an EVA where all traffic was routed through the A controller.

Even if you modified the path preferrence to B, the MPIO did ignore it and the EVA moved the virtual disk ownership to the A controller after some time.

You had to set up a single preferred path on the MPIO to do a manual 'load balancing' between controllers.
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CLEB
Valued Contributor

Re: MPIO Load Balance Policy and ALB relationship

I have a BL460c G1 server connected to an EVA4400. This has a boot from SAN install with Windows 2003 R2 SP2. The LUN is set to No preference for Preferred path/mode.

The MPIO DSM Manager is currently set to SQST with ALB off.

Is it recommended to turn on ALB?

samo69
Occasional Visitor

Re: MPIO Load Balance Policy and ALB relationship

Hi,

Sorry for the hijack..

I'm in a similar position with bl685c's and an eva8000. We are seeing I/O wait requests on a busy SQL box and I believe the MPIO to be at the core of the issue.

Is it recommended to have ALB enabled for performance?
Beer Grill
Advisor

Re: MPIO Load Balance Policy and ALB relationship

Dave Harrold
Advisor

Re: MPIO Load Balance Policy and ALB relationship

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