I recently had a discussion with a vendor (who shall remain nameless) as to whether we really needed Quality of Service in shared storage arrays.  His thinking went as follows; if we have a storage array and network with sufficient bandwidth/IOPS, then why bother implementing QoS?  At first this seems like a reasonable assumption; if I have more resources than required, what’s the problem as I can cater for all requirements.  To think this through as to whether this makes sense, let’s step back and look at how persistent storage…