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dclark
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Active/passive SAN - MRU or Preferred path

Hello

Running ESX3.0.1

We have a CX300 which is active/passive. I understand the recomendation for failover policy is MRU to avoid path thrashing. I can see that this is the best option if you only have one ESX host, but how about if you have more than 1?

Scenario

presume we have only 1 LUN

Host ESX01 has two HBA's one connected to CU0, the other to CU1. CU0 is the currently active path and policy is set to MRU.

Host ESX02 also has 2 HBA's, one connected to CU0, the other to CU1. CU0 is the currently active path and policy is set to MRU.

Now, if we lose the path from ESX01 to CU0 the LUN will move to CU1. That will then become the active path to the LUN from host ESX01, and as we are MRU it will remain the active path.

However ESX02 is still happily using CU0 to access the LUN, and as that is also MRU won't it carry on using CU0?

Am I right in thinking this scenario would lead to constant path thrashing?

OR

Would ESX02 detect that the LUN had trespassed onto a different controller and start accessing it via CU1?

Many thanks.....

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wobbly1
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in this situation the lun will have transitioned to cu1 and therefore esx2 will also failover to this controller path

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wobbly1
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in this situation the lun will have transitioned to cu1 and therefore esx2 will also failover to this controller path

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DFATAnt
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I've been advised by VMware in the past that they recommend MRU (I was using a HDS Thunder).

I've had number of ESX servers (approx 40) with groups of 5 accessing the same shared LUNs and had no problems or path thrashing using MRU.

I sure that if you spoke to VMware they would advise you of the best practice for the type of storage you are using.

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dclark
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Thanks for the updates...

We have two storage arrays, a CX300 and a HDS9570. With the 9570 I have seen path thrashing with MRU set. Perhaos I need to progress with HDS...

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jlauro
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Reading various HCL from Vmware, all I can say is it depends on your SAN. I seen vmware make different recommendations in the same document for different Active/passive SANs. In general, most often, they recommend MRU.

The only bad thing about preferred, is it can cause path thrashing in the event of a failure of the fabric, such that some host can still take the preferred route, and some hosts can not.

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vmmeup
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VMware recommend's using MRU with Active/Passive and Fixed with Active/Active. Actually it is even a question that they cover on the exam. I don't understand why you wouldn't want to run Active/Active and evenly distribute your luns over different path's. But that's just my opinion.

Sid Smith ----- VCP, VTSP, CCNA, CCA(Xen Server), MCTS Hyper-V & SCVMM08 [http://www.dailyhypervisor.com] - Don't forget to award points for correct and helpful answers. 😉
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pcomo
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Hi,

How did you make your Switch zoning and HBA link?

We need to have 4 path/shared LUN to your ESX.

HBA1 need to have one path to Array SP1 and one path to Array SP2, same for HBA2. I this case if one HBA failure occured on one ESX server, esx server could access the LUN by the same CTL but to the second switch Fabric.

Thanks.

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