It would depend on the buffer size being used. In Andre's case he reported it was ok with non-2.0 speeds, probably just luck that the buffer on his disk is large enough that it works ok.
In general I have never had good luck with sync providing anything resembling a decent speed except with raid subsystems that have battery backed-up caches and/or return done the moment it gets into its cache (whether safe or not).
On Fri, Aug 16, 2024 at 1:25 PM Barry Scott barry@barrys-emacs.org wrote:
On 16 Aug 2024, at 18:12, Roger Heflin rogerheflin@gmail.com wrote:
So here is why sync sucks only on a usb 2.0 connection.
The report that lead to the revert of the sync change was on 3.0 connections. The slow down was x10 or more.
So no this is not a USB 2 only issue.
Only if the user program and the USB device can overlap I/O do you get the max speed. If the user space program has to wait on the previous write then you always see a dramatic slowdown.
Barry
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