Before revision:  We also derive an M/G/1 queue approximation for the system, and show with simulations that it performs well in estimating the actual system performance .
After revision:  We also derive an M/G/1 queue approximation for several special cases of interest. Via numerical simulations, we evaluate our bounds, and demonstrate that the M/G/1 queue approximation has a high degree of accuracy. We also compare availability codes with MDS and replication codes .