Whilst reviewing the new ESX4 Web Admin Guide last night, I came across a “new feature”. If you log into a ESX4 WebAccess session and add a new disk to a VM, you have the option to change the “Write caching” policy from the GUI. This option isn’t available from the vClient view.
After a bit of investigation, if you go with the “Optimize for Safety” option (the default), it adds the line scsi0:1.writeThrough = “TRUE” in the vmx file. If you select the “Optimize for Performance”, then it omits this line. Interestingly if you use the vClient to add a disk, it doesn’t add this line.
This means that by default, adding a disk via ESX4 webAccess produces different results than doing it via the vClient. I suspect this is an option which was removed from the vClient, but they forgot to remove it from the webAccess.