VD-IT2, Virtual Disk Cloning on Disk Arrays Using a Type-2 Fuzzy Controller

Abstract

Disk arrays provide data storage by combining sets of disks into one or more virtual disks (VDs) utilizing specialized control algorithms. A VD is a partition of such combined storage capacity perceived by the user as a physical disk. VD cloning is a data protection technique that copies the data from one VD to another. A typical problem with VD cloning is that it delays user reads and writes, i.e., increases response times. This paper presents VD- Interval Type 2 (IT2), an effective IT2 fuzzy logic control (IT2 FLC) approach to VD cloning that dramatically reduces the response time delay. The VD-IT2 cloning scheme is capable of balancing two adversely affecting processes: VD cloning and user read/write response times. This IT2 FLC-based approach regulates throughput of VD cloning with regards to the user request activity. The VD-IT2 solves the increased delay in user reads and write during cloning by adjusting the time interval between cloning requests. The contribution of this paper is two-fold. First, a novel formula for planning of data backups is presented. The data backup formula predicts the fraction of replicated data blocks in a combined (clone and snap) replication. Second, a novel IT2 FLC scheme reduces response time of user reads/writes in half. The VD-IT2 was tested on an Itanium workstation with 120 disks and proved 50% reduction of user latencies within a short period of time (high response time of 60 ms was reduced to half, within 30 s only), on an average basis.