FuSnap: Fuzzy Control of Logical Volume Snapshot Replication for Disk Arrays

Abstract

This paper presents FuSnap, a fuzzy-logic-based controller that monitors and controls the snapshot process of a logical storage volume in a disk array. As disks do not linearly respond to the arrival rate of user accesses, FuSnap makes use of fuzzy logic as the means to achieve better control of their response time. The goal of the FuSnap controller is to reduce the response time caused by the copy-on-writes (CoWs) that occur during the snapping of a storage logical volume. The FuSnap controller, based on the response time of user accesses, makes the decision on whether to proceed with a CoW or a redirect-on-write when a source logical volume is being copied to a snapshot logical volume. The benefits of FuSnap approach are twofold. First, significant reductions in response time of user requests are obtained with the FuSnap approach over the traditional CoW snap approach. Second, these reductions in response time make the point-in-time copy of data a process less disruptive for database users. FuSnap was verified with two setups using Hewlett-Packard UniX workstations, one setup with eight and the other with 32 disks.