Unfortunately, there are some ESXi 5.1 trigger Purple Screen of Death (PSOD) in their production environment on last week. The server model of ESXi host is Cisco UCS Blade Server and edition is VMware ESXi 5.1.0 build-2191751. There are 3 x ESXi 5.1 host is running on Cisco UCS B200M3, all ESXi 5.1 hosts trigger PSOD at same time. Firstly I think it is storage issue. For safety I opened VMware and storage suppor request. Finally the root cause is the related the cisco fnic driver, which is replied from VMware support. This is a known issue with the Cisco fnic driver version 220.127.116.11 when resetting the Storage Processor (SP) on the storage array. The detail as the below KB.
To resolve this issue, upgrade to the latest fnic async drivers, available at VMware Downloads.
Note: It is strongly recommended to contact Cisco directly to confirm proper compatibility before upgrading the drivers. Customers should not update the driver without updating the firmware that supports it.