Why does a USB flash disk refuse to boot? A great mystery...

ikevin8me

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I'm experiencing something strange the two USB flash disks:
(1) an 8GB USB flash disk
(2) an 16GB USB flash disk
... both are from the same manufacturer.

I downloaded FreeBSD-13.0-RELEASE-amd64-dvd1.iso using a Mac, and executed the same command below to write to the two USB flask disks:
# dd if=FreeBSD-13.0-RELEASE-amd64-dvd1.iso of=/dev/da0 bs=1m conv=sync

The 8GB disk refuses to boot up. I've tried doing it a few times and the result is the same.
The 16GB disk always boot up fine.

However, the 8GB disk can be formatted as FAT and works really fine for copying data files between the Mac and the FreeBSD machine.

It's really puzzing what's wrong with the 8GB disk as the process to burn the FreeBSD-13.0-RELEASE-amd64-dvd1.iso is exactly the same for both 8 GB and 16 GB disks.

Why does the 8 GB disk refuses to work as a boot up disk?

If the 8 GB disk is corrupted, why does it function so well as a data transfer disk?

This is a great mystery to me. Anyone has some insights?
 
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ikevin8me

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But I used exactly the same port on the Mac to prepare (ie. burn) the USB sticks! So, the mystery is still unresolved. :)
 

mark_j

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Look on the machine where you used dd in the /var/log/messages file to see if there's any messages for the period when you burnt the 8GB USB drive. Concomitantly, try using dd again on the 8GB drive to see if you achieve the same result of a non bootable drive while watching the /var/log/messages file ( tail -f /var/log/messages)?

Incidentally, what's the error you get? Refuses to boot you say? That's vague.
 
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ikevin8me

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Oh, I re-installed the OS and lost the previous messages file. Perhaps I can try again on another occasion.

Incidentally, what's the error you get? Refuses to boot you say? That's vague.
Refuse to boot up means it will pop back to the BIOS screen (the main disk had been completely wiped).
 

mark_j

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Sounds like it doesn't have the boot blocks correctly written. That might infer your USB disk is heading towards USB heaven?
 
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ikevin8me

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Sounds like it doesn't have the boot blocks correctly written. That might infer your USB disk is heading towards USB heaven?
That’s what I thought too. But… The “problem” is that disk is working very well for transfer of data files. Should I consider that disk as faulty and just throw it away?
 

Trihexagonal

Son of Beastie

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I downloaded FreeBSD-13.0-RELEASE-amd64-dvd1.iso using a Mac, and executed the same command below to write to the two USB flask disks:
# dd if=FreeBSD-13.0-RELEASE-amd64-dvd1.iso of=/dev/da0 bs=1m conv=sync
Your syntax is wrong and you're using the wrong medium for a USB stick, though I know it can be done.
Code:
# dd if=FreeBSD-13.0-RELEASE-amd64-dvd1.iso of=/dev/da0 bs=1m conv=sync

# dd if=./FreeBSD-13.0-RELEASE-amd64-memstick.img of=/dev/da0 bs=1m conv=sync
 

sko

Aspiring Daemon

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However, the 8GB disk can be formatted as FAT and works really fine for copying data files between the Mac and the FreeBSD machine.

That’s what I thought too. But… The “problem” is that disk is working very well for transfer of data files. Should I consider that disk as faulty and just throw it away?

It "works" because FAT doesn't give a damn about data integrity and just returns anything it finds on a given location. Just because you can "copy some file from FAT" doesn't mean you've actually got the correct data and the medium is working correctly.
I've been using ZFS on most USB sticks for several years now, and the rate at which they begin to return wrong data is alarming - around 1/4 of them don't even last for 2 years with very mild use before checksum errors are piling up. and no, those aren't cheap noname devices, which usually do the right thing and just die, but kingston or sandisk...

Apart from that: as Trihexagonal already pointed out, the iso files are not intended for use with flash drives; use the memstick images for that.
 
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