Link: Scalable Storage Performance with VMware ESX Server 3.5 – VMware VROOM!.
It is clear from Figure 1 that except for sequential read there is no drop in aggregate throughput as we scale the number of hosts. The reason sequential read drops is that the sequential streams coming in from different ESX Server hosts are no longer sequential when intermixed at the storage array, and thus become random. Writes generally do better than reads because they are absorbed by the write cache and flushed to disks in the background.
