This paper addresses the unpredictable service availability of large centralized storage solutions. Fibre Channel is a common connection type for storage area networks (SANs) in enterprise storage and currently there are no standard mechanisms for prioritizing workloads using this technology. However, the increasing use of TCP/IP based network communication in SANs has introduced the possibility of employing well known techniques and tools for prioritizing IP-traffic. A method for throttling traffic to an iSCSI target server is devised: the packet delay throttle, using common TCP/IP traffic shaping techniques. It enables close-to-linear rate reduction for both read and write operations. All throttling is achieved without triggering TCP retransmit timeout and subsequent slow start caused by packet loss. A control mechanism for dynamically adapting throttling values to rapidly changing workloads is implemented using amodified proportional integral derivative (PID) controller. An example prototype of an autonomic resource prioritization framework is designed. The framework identifies and maintains information about resources, their consumers, response time for active consumers and their set of throttleable consumers. The framework is exposed to extreme workload changes and demonstrates high ability to keep read response time below a predefined threshold. It exhibits low overhead and resource consumption, promising suitability for large scale operation in production environments.
['Jarle Bjorgeengen', 'Hårek Haugerud']
Using TCP/IP traffic shaping to achieve iSCSI service predictability