SD Card reliability (again)
Heater.
Posts: 21,230
Over time I have heard a lot said about the reliability of SD cards. About wearing out the flash chips about the compensating wear leveling with the cards, about how we should not worry so much...
BUT here I am with a pile of new but unusable micro SD cards and a seemingly impossible task. All I want to do is clone, that is block for block copy, one 4GB SD card to one or more others. The source SD card contains two partitions, one FAT and one Linux ext3 but that should have no bearing on the issue. My approach to cloning is to use the "dd" command under Linux.
So first:
$ dd if=/dev/sdd of=card.img
Then check the copy is good with:
$ md5sum /dev/sdd card.img
OK, so replace the card reader with an empty one and write to it:
$ dd if=card.img of=/dev/sdd
And check the card is a good copy:
$ md5sum /dev/sdd card.img
FAIL!!!
Just in case try to boot my target system with the new copy, FAIL.
For now my original still boots a working target but I get more and more nervous as I can't back it up and restore it.
After a few goes around this loop with new Kingston and SanDisc cards I wonder if it is possible to ever find one that works.
Or am I doing something wrong? This method always used to work for compact flash cards.
BUT here I am with a pile of new but unusable micro SD cards and a seemingly impossible task. All I want to do is clone, that is block for block copy, one 4GB SD card to one or more others. The source SD card contains two partitions, one FAT and one Linux ext3 but that should have no bearing on the issue. My approach to cloning is to use the "dd" command under Linux.
So first:
$ dd if=/dev/sdd of=card.img
Then check the copy is good with:
$ md5sum /dev/sdd card.img
OK, so replace the card reader with an empty one and write to it:
$ dd if=card.img of=/dev/sdd
And check the card is a good copy:
$ md5sum /dev/sdd card.img
FAIL!!!
Just in case try to boot my target system with the new copy, FAIL.
For now my original still boots a working target but I get more and more nervous as I can't back it up and restore it.
After a few goes around this loop with new Kingston and SanDisc cards I wonder if it is possible to ever find one that works.
Or am I doing something wrong? This method always used to work for compact flash cards.
Comments
Verify that they can actually take the correct amount of data by copying in large files...
Go to http://oss.digirati.com.br/f3/
download and compile. Works under Linux. This tool (write first, then read) will check if your cards are good or fake. And it does a read+write+checksum test, just as you're trying to do, so should be very relevant.
-Tor
No not sure at all. Came from a reputable store. But now a days even they can't be sure.
Tor,
Great, never heard of f3 before, it's doing it s thing here now. May take a while...