Your VNXe has a backup battery that will last long enough for all the data in memory to be dumped to the disks.  You can just let it die and it won't cause any issues.  They will come back up and see the dump file and put things exactly as they were before they died.
Hi all,   I've got a 3100 that we are using for vsphere5 storage and I'm busy creating a DR plan for lets assume a power outage. At the moment I've got our UPS kicking off scripts to shutdown vm's and send alert emails but I was wondering about the storage. I see you can login to the vnxe through ssh and possibly script something but I wondering what is the safest option.   Lets assume that our UPS's can keep the infrastructure running for around 15-20 minutes and the mass shutdown of VM's would take around 5 of those minutes and another couple for our 2 esxi hosts to poweroff, would it be a good idea to try and reboot the SP's into service mode before the power dies or just let the running storage die if the batteries drain. Its a case in my mind of which one is less dangerous than the other.  Regards  Dale 
Best to let storage die or attempt service reboot?