If the performance of your hardware bus adapters (HBAs) is unsatisfactory or your SAN storage processors are overutilized, you can adjust your ESXi hosts' maximum queue depth value. The maximum value refers to the queue depths reported for various paths to the LUN. When you lower this value, it throttles the ESXi host's throughput and alleviates SAN contention concerns if multiple hosts overutilize the storage and fill its command queue.
In a way, this solves the problem, but on the other hand, it just pushes the problem closer to the demand. Now, instead of the SP failing to deliver all of the I/O power that is required, it's the hosts that are failing to deliver I/O as fast as the VMs want. Tweaking queue depths is mostly ...
