second boot == Read-only file system

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Re: second boot == Read-only file system

Unread postby odroid » Sat Jan 02, 2016 9:51 am

What is the result of dd test?
Code: Select all
$ dd if=/dev/zero of=test.tmp oflag=direct bs=500K count=1024
$ dd if=test.tmp of=/dev/null iflag=direct bs=500K count=1024

We could get around 15MB/sec of writing speed and 30MB/sec of reading speed with a Sandisk Class10 UHS-1 card on C1+.
I think we could get around 20~25MB/sec of reading speed if we limited the clock at 40Mhz.
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Re: second boot == Read-only file system

Unread postby dchang0 » Sat Jan 02, 2016 11:28 am

The system is so unbearably slow I can't even get as far as running the dd tests. I have reimaged it and used just the "comment out setenv disableuhs "disableuhs"" trick, but that went to read-only filesystem again in the middle of the first apt-get upgrade. I'll add the fdt line and see how it goes.

No luck--it won't get past the reboot. Same error.

I am wondering if it would be smart to send this card back to Samsung and get a replacement on the off chance I might get one that works like the ones you bought... That won't help diagnose the problem with this card, though. Do you have any other commands you want me to run to help identify what is wrong with this particular card? I will try to run the dd commands again, if I can get that far.
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Re: second boot == Read-only file system

Unread postby dchang0 » Sat Jan 02, 2016 11:56 am

I can't run the dd command on the second try either. This is what I get:

Welcome to Ubuntu 14.04.3 LTS ( )

* Documentation: https://help.ubuntu.com/
Last login: Sat Jan 2 12:41:38 2016 from augustus3
-bash: groups: command not found
/usr/bin/lesspipe: 1: /usr/bin/lesspipe: basename: not found
/usr/bin/lesspipe: 1: /usr/bin/lesspipe: dirname: not found
/usr/bin/lesspipe: 295: [: =: unexpected operator
odroid@odroid:~$ dd if=/dev/zero of=test.tmp oflag=direct bs=500K count=1024
-bash: /bin/dd: cannot execute binary file: Exec format error
odroid@odroid:~$

The system isn't even getting to a desktop yet (I had to ssh in to try the above). I think we can safely say that the fdt command does not work at all (makes things worse than just commenting out disableuhs).
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Re: second boot == Read-only file system

Unread postby dchang0 » Sat Jul 22, 2017 3:42 pm

Very belated follow-up.
I found out the Samsung EVO microSDXC 64GB card I bought is a fake. It was packaged perfectly and looks totally legit, but it is corrupting data copied beyond the first 8GB.
It reads and writes up to 64GB, but the data that comes back is bad.
I confirmed it using the freeware tool h2testw.
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Re: second boot == Read-only file system

Unread postby mad_ady » Sat Jul 22, 2017 6:48 pm

Ouch, that was not taken into considerations during the tests
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Re: second boot == Read-only file system

Unread postby dchang0 » Sun Jul 23, 2017 2:14 am

Reading more posts online, apparently, there was a huge batch of fake Samsung EVO 64GB microSD cards made by a Chinese scammer. I can say they were made and packaged so well that they could fool retailers and distributors. My advice to anyone considering this particular model of card is to avoid them unless you can get a rock-solid return policy from the seller. Reading some of the Amazon reviews of the Samsung EVO+ and other newer models, there are fakes of those too.

Anyway, here's what happens: Writing the first image works because it is usually smaller than 8GB. When the image boots up the first time and expands to 64GB, it corrupts itself, which then causes failures on the second boot, etc. This occurs even on a Raspberry Pi as well as my ODROID C1+. I would say to anyone experiencing "second boot == Read-only file system" to immediately test the card to see if it is a fake, because the failure will behave consistently in this manner.

Also, one more technical point: because the filenames are stored in the FAT, the fake card looks like it has successfully written files past the first 8GB, so you will only know the files have been corrupted by actually opening them and checking the contents. That's how I was fooled the first time--I wrote the data, saw the filenames, but did not check the files for corruption. The corruption may be subtle! Opening the file and just glancing at it is not enough. You should test it byte for byte (or use checksums).
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Re: second boot == Read-only file system

Unread postby odroid » Sun Jul 23, 2017 1:59 pm

This "FakeFlashTest" tool was used to detect a bad flash storage for many people too.
https://sites.google.com/a/rmprepusb.co ... ory-drives
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