Check which SATP ESX detects to use for your array, each SATP has a default PSP like fixed, MRU or RR. The default SATP/PSPs are also listed on the HCL for each storage array.
If your array supports ALUA, then ESX should default to the generic ALUA-aware SATP called VMW_SATP_ALUA which uses MRU as the default PSP. If your storage array or vendor supports RR too, you should be able to safely change the PSP to RR. You might want to set a custom IOPS limit for RR too.
Here are some more infos for HP EVA arrays, which are AA and support ALUA with RR:
http://www.ivobeerens.nl/?p=465
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