The speed impact of having a few thousand files in a folder is pretty well known. The drive could have 10% used but the 20,000 files in a folder would make it feel like the drag chute and anchors were deployed.
My friend told me along time ago that solid state drives have to be kept 25% empty in order for them to operate at their quickest. I just got a brand new USB 3.0 flash drive and want it to work its fastest.

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