There are two plots in this figure, one for the ADF data format and one for the HDF5 data format, both showing the I/O time in seconds vs the number of points per zone. Each plot has five curves, corresponding to results for 1, 10, 100, 1000, and 10000 zones.

For the ADF data format, the time for the single-zone case stays below about 2 seconds as the number of points per zone ranges from 100 to 108, then jumps to about 52 seconds at 109 points per zone. For the 10 zone case, the time stays below 2 seconds as the number of points per zone ranges from 100 to 107, then jumps to about 20 seconds at 108 points per zone. The results for the 100 and 1000 zones cases are similar to the 10 zone case, except the jump to 20 seconds is offset to the left by a factor of 10. I.e., jump to 20 seconds occurs at 107 points per zone for the 100 zone case, and at 106 points per zone for the 1000 zone case. For the 10000 zone case, the time stays at 28-29 seconds for 100, 1000, and 10000 points per zone, then jumps to about 47 at 105 points per zone.

For the HDF5 data format, the results for the cases with 1, 10, 100, and 1000 zones are essentially the same as for the ADF data format. For the 10000 zone case however, the time is about 32 seconds for 100 points per zone, jumps to between 74 and 76 for 1000 and 10000 points per zone, and jumos again to about 90 for 105 points per zone.