dataload time is too big but i have used the bin method to load img？

[Lininggggggg]

dear author, do you know why the dataload time is so big even though i have used the binary method to load imgs？, just like the picture 2 and my ram is enough, just like the picture 2

thank you very much!!!

[Lininggggggg]

what's more, only when i set the batch-size is 3, every miniepoch time of the data load time is only need 0.1s, however if i set the batch-size is more than 3, like 13, the time will need about 20s.