  Leader-based data replication improves consistency in highly available
distributed storage systems via sequential writes to the leader nodes. After a
write has been committed by the leaders, follower nodes are written by a
multicast mechanism and are only guaranteed to be eventually consistent. With
Age of Information (AoI) as the freshness metric, we characterize how the
number of leaders affects the freshness of the data retrieved by an
instantaneous read query. In particular, we derive the average age of a read
query for a deterministic model for the leader writing time and a probabilistic
model for the follower writing time. We obtain a closed-form expression for the
average age for exponentially distributed follower writing time. Our numerical
results show that, depending on the relative speed of the write operation to
the two groups of nodes, there exists an optimal number of leaders which
minimizes the average age of the retrieved data, and that this number increases
as the relative speed of writing on leaders increases.
