VMFS LUN sizing notes
Creating a one LUN to one VM
You can get the best performance with 1 VM to 1 LUN/VMFS mapping. There is no competition between machines on the same VMFS, each load is separated and all is good.
The problem is that you are going to manage an ungodly amount of LUNs, may hit supported maximum limits, face headaches with VMFS resizing and migration, have underutilized resources (those single percentage point free space on VMFS adds up) and generally create a thing that is not nice to manage.
Creating one LUN for all VM
The other extreme is one big VMFS designated to host everything. You’ll get best resources utilization that way, there will be no problem with deciding what do deploy where and problems with VMFS X being a hot spot while VMFS Y is idling. Maintenance is an issue since bringing down the one and only LUN means taking down the only storage available to the VMware environment, all the eggs are in one basket so to speak.
The accepted practice is to create datastores large enough to host a number of VMs and divide the available storage space into appropriately sized chunks. What the number of VMs is depended on the nature of the VMs. You may want a single or a couple of critical production data bases on a VMFS, but allow three or four dozen of test and development machines onto the same datastore.