  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.
