Abstract: Cloud storage has gained massive popularity in the IT industry. It has proven to be cost effective and reliable. Research has shown that striping of data across multiple cloud vendors is a remedy for providing fault tolerance. In case the cloud suffers from a permanent failure it leads to loss of data in the cloud. In this scenario the lost data can be repaired or recovered using the other surviving clouds. This multiple cloud-storage system is called a Network-Coding based cloud storage system. NC Cloud is a proxy based system which provides fault tolerance and provides cost-effective repairs for systems which suffer from permanent single-cloud failure. The NC Cloud is built on top of Functional Minimum Storage Regenerating (FMSR) codes which provide the same fault tolerance as traditional erasure codes like RAID 5 and RAID 6 but use less data repair traffic. Therefore, the FMSR codes provide significant cost savings in repair over RAID 6 codes but have similar performance during upload and download of data. The concept of Network-Coding based cloud storage is gaining mass popularity due to its desirable properties like data recovery, cost effectiveness and fault tolerance.
Keywords: FMSR codes; NC Cloud; Fault tolerance; data recovery; regenerating codes; Traditional erasure codes; Mean-time-to-data-loss (MTTDL); MDS property.