On 2021-03-02 1:37 a.m., Frederic Muller wrote:
So I was wondering if there was any logical explanations and things I
could do to ensure I use the disk at its maximum speed.
You are using Fedora, so you have an already-installed graphical utility
to run a quick benchmark test on the disk. You can find the disks
utility (usually in the utilities icon), select the appropriate disk on
the left, and click on the "..." on the top right. You will see a
benchmark selection. Start that up and it will run for about a minute,
checking random and sequential read and write times, and graphing it
nicely for you. Since the disk is on a USB port, you need to be careful
about getting the rest of the machine as idle as possible, as almost all
USB implementations are CPU-bound.
If you're not getting the specified speeds, then it could be due to a
number of factors that are probably unrelated to the disk itself.
However, one thing will affect your write speeds: most SSDs have a cache
system onboard to mitigate slow write speeds. Writing a much larger file
than the RAM buffer in the disk will result in stalling that looks like
what you are describing. That's not unexpected, but it does lead to the
next problem - what happens if power is lost while writing. Is the
drive's onboard cache flushed, or is it lost due to an onboard lack of
large power capacitors as a cost reduction? If the latter is true, then
this is a point where you're going to appreciate that your use of BTRFS
or ZFS will at least prevent disk corruption in this situation. Note
that the drive cost is not related to the answer, as e.g. expensive
Samsung EVO drives are known to have this issue.
--
John Mellor
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