@alfaunits
Whether the random data generator is producing 10MB/s or 100MB/s has nothing to do with writing randomly or not.

The Areca can sustain those speeds until the cache is filled or as long as the array can sustain that speed, I was using a small array incapable of coping with that speed and thus it wasn't sustained. (it lasted for a few seconds)
The easy test is just to generate the random data without writing the data, that would tell the potential of the random "generator".

Anyways this is out of topic, a separate thread would be needed and I haven't got the time right now.

@Ao1
We can only presume but that's the general idea of write combining.
If the file spanned the whole drive everything would be random per say, what we have been doing so far is just producing writes (both small and large files) but no random IO within those files.
Random writes withiin a file overwrites data in stead of just writing a new file, there is a huge difference between those two scenarios.

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Link to Anand