If you’ve tried to update the vnxe firmware and the update has failed (usually around the 21% mark). Then you will find that the write cache will not be re-enabled until the software update has completed sucessfully. Now when i’ve had this issue emc have stated that its because of a hung process but I found that restarting storage processors do not cure the issue. What I did to resolve the error was to put both storage processors in service mode and then pull the power out of both sp’s.
Once the vnxe is completely bereft of power the plug both back in and wait for it to boot, take the sps’s out of service mode and re attempt the software update. It should go through without any further issues.
Its essentially the old turn it off and on again solution.