Although there are no steadfast rules for how many virtual machines should be placed on a datastore due to the scalability enhancements of VMFS-5, a good conservative approach is to place anywhere between 15-25 virtual machines on each.

The reasoning behind keeping a limited number of Virtual Machines and/or VMDK files per datastore is due to potential I/O contention, queue depth contention, or Legacy SCSI reservation conflicts that may degrade system performance.

This is why I suggest limiting your datastore size to 500GB-700GB each, because this helps limit the total number of virtual machines that can be placed on each datastore.

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