In my blog post: “HP CA and the use of LUN balancing scripts” I tried to cover the possible impact of using HP continuous Access EVA on the LUN path load balancing scheme in ESX 3.x. I received a lot of questions about this and wanted to address some issues again and try to clarify them. Let’s begin with a recap of the HP CA article; The impact of CA on the load-balancing scheme is due to the fact that an EVA is an asymmetric Active-Active array that uses the Asymmetric Logical Unit Access protocol (ALUA). ESX3 is not ALUA aware and does not recognize the different specific access characteristics of the array’s target ports. VMware addressed this shortcoming and added ALUA support in the new storage stack of ESX4. The ALUA support is a great feature of the new storage architecture, it reduces a lot of extra manual steps of creating a proper load-balanced environment. But how exactly does ALUA identifies which path is optimized and will HP Continuous Access still have an impact on ESX4 environments as well?
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HP CA and the use of LUN balancing scripts
Some of my customers use HP Continuous Access to replicate VM data between storage arrays. Lately a couple of LUN balancing powershell- and Perl scripts were introduced in the VMware community. First of all, there is nothing wrong with those scripts. For example, Justin Emerson wrote an excellent script that balances the active paths to an active/active SAN. But using an auto balance scripts when Continuous Access is used in the Virtual Infrastructure can result in added IO latency and unnecessary storage processor load. Here’s why: [Read more…] about HP CA and the use of LUN balancing scripts