Re: Understanding SD data transfer

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On Mon, 24 Jul 2023 14:53:15 -0700
Samuel Sieb <samuel@xxxxxxxx> wrote:

> On 7/24/23 14:44, Geoffrey Leach wrote:
> > Fedora 37, up-to-date
> > Controller JMicron Technology
> > Medium 1TB SanDisk ultra SD, sped transfer rate 120MB/sec
> > DATA 155MB
> > df /Media/SDXC says its 26% full
> > 
> > % mount /Media/SDXC
> > % time cp DATA /Media/SDXC
> > real		0m0.145s
> > user		0m0.001s
> > sys		0m0.41s
> > % time cp DATA /Media/SDXC
> > real		2m44.656s
> > user		0m0.002s
> > sys		0m0.211s
> > 
> > I assume that the first cp just 'fills the queue, but  even assuming
> > that I then have 310MB transferring, that's pretty slow.  
> The SD card may support that speed, but the reader might not.  Try 
> running "iostat 1" in another window to see what the actual speeds
> are. 

Hmmm .... well  iostat reports around 1  MB/sec, which is consistent
with the data above. Not what I expected, given the specs on the card

Samuel, thanks.
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