Title: Simplex Queues for Hot-Data Download,
Abstract: In cloud storage systems, hot data is usually replicated over multiple nodes
in order to accommodate simultaneous access by multiple users as well as
increase the fault tolerance of the system. Recent cloud storage research has
proposed using availability codes, which is a special class of erasure codes,
as a more storage efficient way to store hot data. These codes enable data
recovery from multiple, small disjoint groups of servers. The number of the
recovery groups is referred to as the availability and the size of each group
as the locality of the code. Until now, we have very limited knowledge on how
code locality and availability affect data access time. Data download from
these systems involves multiple fork-join queues operating in-parallel, making
the analysis of access time a very challenging problem. In this paper, we
present an approximate analysis of data access time in storage systems that
employ simplex codes, which are an important and in certain sense optimal class
of availability codes. We consider and compare three strategies in assigning
download requests to servers; first one aggressively exploits the storage
availability for faster download, second one implements only load balancing,
and the last one employs storage availability only for hot data download
without incurring any negative impact on the cold data download.