Availability codes have recently been proposed to facilitate efficient retrieval of frequently accessed (hot) data objects in distributed storage systems. This paper presents techniques for analyzing the download time of systematic availability codes considering the Fork-Join scheme for data access. Specifically, we consider the setup in which requests arrive for downloading individual data objects, and each request is replicated (forked) to the systematic server containing the object and all of its recovery groups. For low-traffic regime , when there is at most one request in the system, we compute the download time in closed-form and compare it across systems with availability, maximum distance separable (MDS), and replication codes . We demonstrate that availability codes can reduce download time in some settings , but are not always optimal. When the low-traffic assumption does not hold, system consists of multiple inter-dependent Fork-Join queues, which makes exact analysis intractable due to state space explosion. Here , we present upper and lower bounds on the download time, and an M/G/1 queue approximation for several special cases of interest. Via extensive numerical simulations, we evaluate our bounds , and demonstrate that the M/G/1 queue approximation has a high degree of accuracy.
The paper presents techniques for analyzing the expected download time in distributed storage systems that employ systematic availability codes . These codes provide access to hot data through the systematic server containing the object and multiple recovery groups. When a request for an object is received, it can be replicated (forked) to the systematic server and all recovery groups. We first consider the low-traffic regime and present the close-form expression for the download time . By comparison across systems with availability, maximum distance separable (MDS), and replication codes , we demonstrate that availability codes can reduce download time in some settings but are not always optimal. In the high-traffic regime, the system consists of multiple inter-dependent Fork-Join queues, making exact analysis intractable . Accordingly , we present upper and lower bounds on the download time, and an M/G/1 queue approximation for several cases of interest. Via extensive numerical simulations, we evaluate our bounds and demonstrate that the M/G/1 queue approximation has a high degree of accuracy.
R
Availability codes have recently been proposed to facilitate efficient retrieval of frequently accessed (hot) data objects in distributed storage systems. This
The
R
download time of
expected download time in distributed storage systems that employ
R
considering the Fork-Join scheme for data access. Specifically, we consider the setup in which requests arrive for downloading individual data objects, and each request is
. These codes provide access to hot data through the systematic server containing the object and multiple recovery groups. When a request for an object is received, it can be
R
containing the object and all of its
and all
R
For
We first consider the
R
, when there is at most one request in the system, we compute
and present the close-form expression for
R
in closed-form and compare it
. By comparison
R
. We
, we
D
,
R
When the low-traffic assumption does not hold,
In the high-traffic regime, the
R
which makes
making
R
due to state space explosion. Here
. Accordingly
D
special
D
,