ALUA & VMware multipating

What is the appropriate Path Selection Plugin (PSP) for your ESXi ?

Do not wait... check with your storage vendor. As a VMware administrator, In the past I'd my own reasons to choose Round Robin ahead of MRU and Fixed. But that may not be always good for the below reason.

Each storage vendor has their own method of handling I/O. For all recent Active/Active storage processors (SP), you will see two paths to a given LUN in VMware. But only one processor will actually own the LUN. The path to this storage processor is called as the Optimized path and the path to the other will be Unoptimized path. VMware PSP (MRU and Fixed) will always send its request to the Optimized path and once it reaches the SP, it will internally transfer the request to the other SP. In short ALUA is something which helps the array to service its I/O request using the interconnects between the SP.

In scenarios where the Optimized path fails, VMware vSphere PSP will choose the PSP and failback based on the PSP. If its MRU, it will go back to the Optimized path when it comes back. For Fixed it will continue to run in the same path.

So its better to check with the storage vendor before you configure the PSP.

Hope this gave you some insight to the ALUA story from VMware.


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