University Events

Description: TOPIC: RELIABILITY MODELING AND OPTIMIZATION OF CLOUD-RAID STORAGE SYSTEMS WITH IMPERFECT FAULT COVERAGE

LOCATION: Lester W. Cory Conference Room, Science & Engineering Building (SENG), Room 213A

ABSTRACT:
As a fault-tolerant data storage model, Cloud-RAID (Redundant Array of Independent Disks) utilizes diverse data redundancy techniques (corresponding to different levels) to enhance data reliability and availability in an anytime, anywhere data access framework implemented in the cloud environment. Performance and operation of physical disk drives in a cloud-RAID storage system are managed by and dependent on a controller. Also, each disk may exhibit multiple performance levels varying from perfect function to complete failure. The inter-component dependent behavior and the multistate behavior pose challenges to the reliability analysis of cloud-RAID storage systems. Further complicating the cloud-RAID reliability analysis is the imperfect fault coverage (IFC) behavior, where due to the malfunction of the system recovery mechanism an uncovered component fault may propagate and cause extensive damages to the whole system. Failure to address this behavior can lead to inaccurate (often overestimated) system reliability results, thus misleading the system design, operation and optimization activities. Therefore, it is important to consider the IFC in the cloud-RAID system reliability modeling and analysis.

Existing works on the cloud-RAID system reliability have typically assumed fully reliable fault detection and recovery mechanisms, i.e., perfect fault coverage, which is rarely true in real-world systems. This dissertation research relaxes this assumption through decision diagrams-based combinatorial approaches for the reliability analysis of the cloud-RAID storage systems subjected to the IFC. The proposed methods are applicable to homogenous or heterogeneous disks with arbitrary types of time-to-failure distributions. Two different IFC models are considered: element level coverage where effectiveness of the system recovery mechanism and thus the fault coverage probability rely on the occurrence of each individual element fault, and fault level coverage where the coverage probability relies on the number of element faults happening to a particular group within a certain recovery window. Both binary-state and multi-state disk and system models are addressed. Cloud-RAID 5 and cloud-RAID 6 systems are analyzed as case studies to illustrate effects of dependence, multistate and imperfect coverage factors. Future directions in optimizing the cloud-RAID systems to balance the system reliability and cost are discussed.

NOTE: All ECE Graduate Students are ENCOURAGED to attend.
All interested parties are invited to attend. Open to the public.

Advisor: Dr. Liudong Xing
Committee Members: Dr. Hong Liu and Dr. Honggang Wang, Department of Electrical & Computer Engineering, UMass Dartmouth; Dr. Vinod Vokkarane, Department of Electrical & Computer Engineering, UMass Lowell

*For further information, please contact Dr. Liudong Xing at 508.999.8883, or via email at lxing@umassd.edu.