The present invention provides mechanisms that enable application instances to pass block mode storage requests directly to a physical I/O adapter without run-time involvement from the local operating system or hypervisor. In one aspect of the present invention, a mechanism is provided for handling user space creation and deletion operations for creating and deleting allocations of linear block addresses of a physical storage device to application instances. For creation, it is determined if there are sufficient available resources for creation of the allocation. For deletion, it is determined if there are any I/O transactions active on the allocation before performing the deletion. Allocation may be performed only if there are sufficient available resources and deletion may be performed only if there are no active I/O transactions on the allocation being deleted.