For anyone using Storage IOPs in VMware Cloud Director Tomas Fojta has a great post to explain how it works – VMware Cloud Director for Storage IOPs Management. I encountered a Storage DRS fault of “the available storage IOPs capacity is not sufficient for the operation” that was actually caused by the Cloud Director IOPs limit settings.

Taking a deep dive into Storage IOPs management I discovered setting an IOPs limit in Cloud Director and vCenter act differently. With Cloud Director when setting an IOPs limit, 100% IO reservation is also applied. With vCenter these are independent settings. The IO reservation on a virtual machine can been seen from the StorageIOAllocationInfo.

Back to the Storage DRS fault. As part of the Cloud Director IOPs setup an iopsCapacity field is required on the datastore. vCenter and Storage DRS does nothing with this field. vCenter makes its own calculations on the IOPs capacity of the underlying storage supporting the datastore. As Cloud Director is reserving 100% I0 it important when setting IOPs limiting in Cloud Director that the limit will support the underlying storage. For example my problem was that the datastore could only support 0.25 IOPs per GB but the Storage Policy in Cloud Director was set to 1 IOPs per GB. Hence the Storage DRS fault “the available storage IOPs capacity is not sufficient for the operation” was due to the lack of IOPs capacity to support the IO reservation.