Achieving predictable response time with an intelligent file system updater

Abstract

Delayed write is a very popular technique to improve the file system performance of UNIX operating systems. When write operations are delayed, an update policy decides how and when to write these modified blocks to their assigned disk locations. Recent research results show that conventional update mechanisms do not perform very well, because they neglect the fact that different I/O requests naturally have different characteristics. It makes time critical interactive jobs endure large variations in response time. Update policy controls background write activities that are less time critical and should be performed under constraints that do not violate the urgency of other time critical jobs. In this paper we propose an effective update scheme. We suggest new techniques: burst declustering and opportunistic asynchronous write. Besides, we develop a system activity sensor called SAPRO (system activity probe) that monitors the system activities and disk queuing status to adjust the behavior of our algorithm. Performance evaluation shows that our algorithm can alleviate the lengthy queuing delay, reduce the variance and worst case read response time significantly (30% and 51% respectively). The mean read response time and total system performance are also improved.