Don’t knock ifort too badly, as it has a LOT of options (maybe too many?) for controlling buffer size and default record length with the caveat that you can really eat up memory with some of the defaults. Internal buffering can be very efficient if you can afford the memory use. To paraphrase a little “Oog say buffering good”, but that is one that can be taken to an extreme.
As regards I/O another one is “Oog say ASCII bad. Binary good.” Drives several people crazy including me when sequentially used engineering-scale data is written as ASCII XML in a scratch file instead of sequential binary data when no human is every going to look at the data. If you look at the timing difference there I have seen it be a factor of 200x.
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