`pv` rates (was: burn iso to usb)
Anssi Saari [2021-08-02 19:04:59] wrote:
> David Wright <deblis@lionunicorn.co.uk> writes:
>> On Mon 02 Aug 2021 at 16:14:15 (+0300), Anssi Saari wrote:
>>> Stefan Monnier <monnier@iro.umontreal.ca> 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 </path/to/file.iso >/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. 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).
Stefan
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