On Mon 02 Aug 2021 at 13:26:19 (-0400), Stefan Monnier wrote:
> Anssi Saari [2021-08-02 19:04:59] wrote:
> > David Wright writes:
> >> On Mon 02 Aug 2021 at 16:14:15 (+0300), Anssi Saari wrote:
> >>> Stefan Monnier writes:
> >>> >>> > cp /path/to/file.iso /dev/sdX
> >>> >>> dd if=whatever.iso of=/dev/sdX
> >>> >> It's up to taste.
> >>> >
> >>> > Not at all. The only right answer is:
> >>> >
> >>> > pv -parIe /dev/sdX
> >>>
> >>> Actually I'm not sure how good it is to have both -a and -r, pv doesn't
> >>> really show which rate counter is which...
> >>
> >> No need: the rate is far more variable than its average, as time passes.
> >
> > I guess it depends. Before that comment I tried it on an old USB
> > stick. Read speed was pretty much constant if low. So I think it was the
> > left rate counter that showed current rate but wouldn't bet on it.
>
> [ I'm glad my silly intervention brings up a more constructive
> discussion ;-) ]
>
> If they're both pretty much constant, they're presumably both pretty
> much equal, so it doesn't matter which is which ;-)
>
> But indeed, it's not always the case. I'm right now using `pv` to read
> data off of a broken drive (a 2TB 2½" drive which apparently has
> problems seeking, resulting in a transfer rate of about 45kB/s), and
> it's currently showing me 45.0KiB/s and 70.6KiB/s both of which are
> quite stable.
Writing "quite stable" cloaks the information nicely. The average can
never move away from the rate: a change in the least significant digit
gives the game away.
> If it weren't for the first sometimes changing to
> 44.xKiB/s it'd be hard to know which is which (IIUC the average is
> higher because occasionally the drive gives a more reasonable transfer
> rate than that measly 45kB/s).
So now we're left wondering how you came by this situation. Perhaps
you slumped onto the Return key, then woke up after a few minutes,
having missed the initial burst that gave rise to the average being
more than 50% faster than the current rate.
Cheers,
David.
