  In wireless cloud storage systems, the recovery failure probability depends
on not only wireless channel conditions but also storage size of each
distributed storage node. For an efficient utilization of limited storage
capacity and the performance characterization of allocation strategies, we
asymptotically analyze the recovery failure probability of a wireless cloud
storage system with a sum storage capacity constraint for both high SNR regime
and low SNR regime. Then, we find the optimal storage allocation strategy
across distributed storage nodes in terms of the asymptotic recovery failure
probability. Our analysis reveals that the maximal symmetric allocation is
optimal for high SNR regime and the minimal allocation (with $\lfloor T\rfloor$
complete storage nodes and an incomplete storage node) is optimal for low SNR
regime, where $T$ is the sum storage capacity. Based on the numerical
investigation, we also show that in intermediate SNR regime, a balance
allocation between the minimal allocation and the maximal symmetric allocation
would not be required if we select one between them according to SNR.
