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I have an external USB4 Nvme drive (4TB Crucial P3 Plus NVMe SSD) in a Yottamaster enclosure If I leave black magic speedtest running I note that the transfer rates appear to fluctuate between legacy USB rates and USB3/4 rates fast transfer rate

and slow transfer rate

however the connection mode remains the same in system information and smartmontools reports no errors and temperature of the device is well within tolerance

devices

Im running 15.1.1 and this occurs on my M3 Air as well as my M1 Pro, with and without a USB4 powered hub (Caldigit Elements) If I disconnect and reconnect the drive it always seems to start fast but then slows down and speeds up randomly.

How can I get better diagnostics?

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  • Do you actually notice any slowdown when "really" using the drive, outside of benchmarks? Are you using the drive while also performing the test? Perhaps the maximum speed is only achieved for short bursts on this drive?
    – benwiggy
    Commented Nov 26 at 12:32
  • Good question! I am not using the drive whilst benchmarking it. but I can set up some batch jobs to check io thoughput.
    – Paddy Carroll
    Commented Nov 26 at 13:51
  • Ok in real world testing I still have speed variations of a factor of 10 for reasons unknown, gonna repeat test to double check
    – Paddy Carroll
    Commented Nov 27 at 11:35

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