Please read the arcticle below before upgrading to vSphere 5.1
PowerPath/VE 5.7 and PowerPath/VE 5.7 P01 have not been qualified with vSphere 5.1. Upgrading to vSphere 5.1 may result in unpredictable behaviour.
VMware and EMC have identified a fix for this issue. For customers using PowerPath/VE, VMware recommends not upgrading to vSphere 5.1 until you perform the steps in this article.
Download PowerPath/VE 5.7P02 from EMCPowerLink and contact VMware Technical Support and quote KB 2034796 to obtain a hot-patch for ESXi 5.1.
To upgrade PowerPath/VE 5.7 P02 with vSphere 5.1:
Contact VMware Support and quote KB 2034796 to obtain a hot-patch
Install the hot-patch.
Download PowerPath/VE 5.7 P02 from EMC PowerLink and install it.
If you are already on vSphere 5.1 with PowerPath/VE 5.7 P02:
Install the hot-patch.Note: You may need to reconfigure PowerPath/VE options.
Note: PowerPath/VE 5.7 P02 is a full package release. It can be installed on a fresh ESXi host (that is, a host with no previous version of PowerPath installed) or as an upgrade
For related information from EMC, see EMCKB emc302625.
For information on contacting VMware Support, see Filing a Support Request in My VMware (2006985).
VMware KnowledgeBase link to Article