On a sunny day (Tue, 24 Jul 2018 13:59:00 +1200) it happened
nospam.Henri.Derksen@f1208.n280.z2.binkp.net (Henri Derksen) wrote in
:

>Hello Jan,
mm
You are copying on a raspi???
Using external card reader with 2 slots?
What is your hardware setup?


I copy as folows.
power off raspi
take card out
put it in laptop
copy to /dev/zero (for demo card speed)
that is always about the same as what hdparm -t /dev/card says,
no matter what blocksize.
At least on my 8GB card.


If you copy to a file on harddisk, say some.img
then you also need to look at how fast that harddisk goes sector by sector.
USB card readers may do things to speed, especially old ones,
if you saturate the USB2...?

Here some test on my laptop with ever increasing filesize,
card in /dev/sdc  hardisk partition is /dev/sda5  destination file q1
card is latest 32 GB Samsung cllass 10 or sometging that I mentioned in this
thread before.
do not have more free space ATM, but no real differences:


~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=1 bs=1M
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0687257 s, 15.3 MB/s

~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=2048
2048+0 records in
2048+0 records out
1048576 bytes (1.0 MB) copied, 0.080926 s, 13.0 MB/s


~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=10 bs=1M
10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 0.622834 s, 16.8 MB/s

~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=20480
20480+0 records in
20480+0 records out
10485760 bytes (10 MB) copied, 0.6317 s, 16.6 MB/s


~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=100 bs=1M
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 6.85355 s, 15.3 MB/s

~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=204800
204800+0 records in
204800+0 records out
104857600 bytes (105 MB) copied, 6.79278 s, 15.4 MB/s
dd if=/dev/sdc of=/mnt/sda5/q1 count=1000 bs=1M  0.01s user 5.44s system 6% cpu
1:18.03 total


~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=2048000
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 68.2988 s, 15.4 MB/s
dd if=/dev/sdc of=/mnt/sda5/q1 count=2048000  0.58s user 9.93s system 15% cpu
1:08.57 total

~ # dd if=/dev/sdc of=/mnt/sda5/q1 count=1000 bs=1M
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 69.051 s, 15.2 MB/s


The card read speed:
# hdparm -t /dev/sdc

/dev/sdc:
 Timing buffered disk reads:  46 MB in  3.10 seconds =  14.82 MB/sec
panteltje10: /mnt/sda5 # hdparm -t /dev/sdc

/dev/sdc:
 Timing buffered disk reads:  46 MB in  3.10 seconds =  14.83 MB/sec


The harddisk read speed:
# hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 338 MB in  3.00 seconds = 112.64 MB/sec
panteltje10: /mnt/sda5 # hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 370 MB in  3.01 seconds = 123.02 MB/sec

So, I do not know what all your problems are, but this is get back to basics...

Of course you should not do the copy on a rapi itself, it is not a real
computah ;-) ;-) ;-)

And it is just data, sector by sector, does not matter what is on it.

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