The Scottish Boinc Team

Posted: **Tue Sep 10, 2019 5:31 pm**

Whenever and wherever I buy SD cards, I always perform a full write / read / compare cycle on them. This is because many have been hacked to report a much higher capacity than they actually have. Typically, you can write data to the hacked ones but it isn't there when you read it back. This is not good.

Windows users should use h2testw

On Linux, I use f3write / f3read which operates similarly; it writes a number of 1Gb files until the media is full. Here is a 4Gb card which has been sold as a 32Gb card by this eBay seller https://www.ebay.co.uk/itm/Samsung-32GB ... 2749.l2649

Code: Select all

$ ./f3write /media/david/AC26-2B24
Free space: 28.91 GB
Creating file 1.h2w ... OK!                          
Creating file 2.h2w ... OK!                          
Creating file 3.h2w ... OK!                          
Creating file 4.h2w ... OK!                         
Creating file 5.h2w ... OK!                         
Creating file 6.h2w ... OK!                         
Creating file 7.h2w ... OK!                         
Creating file 8.h2w ... OK!                         
Creating file 9.h2w ... OK!                         
Creating file 10.h2w ... OK!                         
Creating file 11.h2w ... OK!                         
Creating file 12.h2w ... OK!                         
Creating file 13.h2w ... OK!                         
Creating file 14.h2w ... OK!                         
Creating file 15.h2w ... OK!                         
Creating file 16.h2w ... OK!                         
Creating file 17.h2w ... OK!                         
Creating file 18.h2w ... OK!                         
Creating file 19.h2w ... OK!                         
Creating file 20.h2w ... OK!                         
Creating file 21.h2w ... OK!                         
Creating file 22.h2w ... OK!                         
Creating file 23.h2w ... OK!                         
Creating file 24.h2w ... OK!                         
Creating file 25.h2w ... OK!                         
Creating file 26.h2w ... OK!                        
Creating file 27.h2w ... OK!                        
Creating file 28.h2w ... OK!                        
Creating file 29.h2w ... OK!                        
Free space: 0.00 Byte
Average writing speed: 7.31 MB/s
$ ./f3read /media/david/AC26-2B24
                  SECTORS      ok/corrupted/changed/overwritten
Validating file 1.h2w ... 2097152/        0/      0/      0
Validating file 2.h2w ... 2097152/        0/      0/      0
Validating file 3.h2w ... 1162688/        0/      0/      0 - NOT fully read due to "Input/output error"
Validating file 4.h2w ...                                  f3read: Can't open file /media/david/AC26-2B24/4.h2w: No such file or directory

Posted: **Wed Sep 11, 2019 12:01 am**

Maybe it just has a 4GB partition on it. Try SD Formatter from here...https://www.sdcard.org/downloads/formatter/

EDIT: Read closer

Maybe it's just a bad card

Posted: **Wed Sep 11, 2019 3:52 am**

Will try that formatter but the symptoms precisely match those I've had in the past.

Posted: **Wed Sep 11, 2019 2:05 pm**

scole of TSBT wrote: ↑Wed Sep 11, 2019 12:01 am https://www.sdcard.org/downloads/formatter/

Very interesting. This does appear to have solved the problem in one of the cards, thank you.

Still planning to return it though as - out of the box with a FAT partition - it failed to work. I could never trust it for critical data I don't think

Posted: **Thu Sep 12, 2019 1:57 am**

To stay on topic: how does one revive a SD card that has fallen to the 'read-only' syndrome?

If you have such a card you get such witty suggestions as:

"Remove "Memory card locked" Error via Lock Switch" Duh, as if I can't come up with that idea. Besides, it doesn't work, the switch is not in 'lock' position.
"Unlock SD Card with Password" Duh, I use no passwords on my cards.
"Remove Write Protection on the SD Card" Duh, tried Windows cmd commands, GParted under Linux and Linux command line: nothing works, it just shows up again as read-only when checking.
"Format the Memory Card" Duh, can't because of 'read-only lock'

The Scottish Boinc Team

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