Optimizing Delay in Delayed-Write File Systems
Peter M. Chen · 2000
Abstract: Delayed writes are used in most file systems to improve performance over write-through while limiting the amount of data lost in a crash. Delayed writes improve performance in three ways: by allowing the file cache to absorb some writes without ever propagating them to disk (write cancellation), by improving the efficiency of disk writes, and by spreading bursts out over time. For each of these benefits, this paper determines the optimal value for the delay interval: the smallest delay that achieves as good (or nearly as good) performance as an infinite delay. The largest value for optimal delay of any of the three benefits is. This value is 1-10 seconds for current systems, implying that the delay used today (30 seconds) is much too large; a smaller delay would minimize data loss yet maintain the same performance. 1