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Re: causes for this?

Is it a new SSD that has not been used before? Did you start copying data shortly after powering it on for the first time?

I saw similar behavior with an SD card a few years ago, and came up with a theory that when new the SSD controller needs to test all the flash to build up a bad blocks map, but most this is not done in the factory, only when the device is powered for the first time.

So when you first plug in a flash device, only a few megabytes are actually available for writing, and the controller is busy running self test routines on the rest. Any writes to the untested parts of the flash get queued behind the testing so will be quite slow. Most users would not notice an effect, especially with SD cards in digital cameras because they are powered all the time and only filled gradually.

Of course this is all just a theory with no real evidence to back it up other than a cynical view of flash drive manufacturers cost cutting, but as a work around I now make a point of plugging in a new drive and leaving it to sit powered but not otherwise in use for a few hours before I start copying large amounts of data.

David Pottage

On 23/06/18 13:39, Gene Heskett wrote:
I have a usb-3 to sata adapter with a 60GB ssd attached plugged into one
of the usb-2 ports of a raspi 3b. I just moved a 150 megabyte zip file
containing the 750 megabyte sources for an rt kernel to it, got decent
speed doing the copy.

ssh'd into the pi, I asked mc to uppack it, took several minutes. When mc
finally displayed the root dir of the data in the zip, I set it to the
task of copying it to the ssd.  The speed slowly decayed and after
around 700k has been copied, the speed is now just over 112  bytes a
second, with an ETA of nearly 2000 hours. Well into August to complete
at this rate.

Does anyone have a clue where the blockage for data might be?  This is
from that drive, to that drive. htop is showing perhaps 1 megabyte of
swap being used. ????????

Thanks everybody.

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
  soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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