I'm using psutils to get disk information and I'm wondering a bit more about disk_io_counters(). Are the numbers that come back each time I make that call accumulative? Or is it the delta between the last time I called it and now? Something else? I've read the docs here and they don't provide much detail in terms of what I'm trying to find out.
On Linux, those counters get their data from the /proc/diskstats file. See https://www.kernel.org/doc/Documentation/iostats.txt for more. They are cumulative and reset when they overflow or the disk that they pertain to is removed or when the computer resets. I can't find a source to support that last statement but it is true.