I personally tend not to recommend anything above 20 VMs in a VMFS.... especially if those VMs are heavily utilised. This is not just for snapshot quiecsing but also for disk IO queues & latency / disk locking.
Jason Boche did a great study on the appropriate number of VMs which is available to read here: VAAI and the Unlimited VMs per Datastore Urban Myth. His conclusion is:
- 10 high I/O VMs per datastore
- 15 average I/O VMs per datastore
- 20 low I/O VMs per datastore
Yeah that's normally my rule of thumb, but I also like to try to push the envelope to make sure I'm making the most of what I have. From an I/O standpoint we really don't see any contention. To give you an idea our 120 VMs on this side of our company averages barely 1800 IOPs during business hours, so I was hoping to stretch it a little bit more, but started running into snapshots not completing. So was just looking for what others were finding success with.