Analyzing the download time of availability codes

In distributed storage systems, a special sub-class of locally repairable codes, referred to as availability codes, has been proposed to enable recovery of each data block from one of its repair groups. A repair group typically contains a small number of nodes and does not overlap with any other repair group of the same data block. Availability codes have several important benefits, including high degree of fault tolerance, efficient recovery from failures, and efficient access to data by multiple users. In this paper, we study the availability codes from a queuing-theoretical perspective. Specifically, we analyze the average time necessary to download a block of data under the Poisson request arrival model in two service/scheduling scenarios. We compare the availability codes with several alternatives such as MDS codes and replication schemes. Our results indicate that availability codes can minimize the download time in some settings, but are not always optimal.