Re: [gentoo-user] Partition of 3TB USB drive not detected

[james <garftd@verizon.net>]

On 08/01/2016 01:45 AM, J. Roeleveld wrote:
> On Sunday, July 31, 2016 03:37:55 PM Jörg Schaible wrote:
>> Hi,
>>
>> for my backups I use a 3TB USB drive (one big ext4 partition) without any
>> problems. Just plug in the cable, mount it and perform the backup. The
>> partition (sdi1) is detected an mountable without any problems:
>>
>> =============== %< ==============
>> $ ls -l /dev/disk/by-id
>> total 0
>
> <snipped bunch of 'ls' statements
>
>> =============== %< ==============
>>
>> However, when I boot a rescue system from a USB stick, the partition on the
>> USB is not detected. I already tried latest SystemRescueCD (default and
>> alternate kernel), Knoppix and the Gentoo Admin CD. Nothing, the partition
>> is not available.
>>
>> What's the difference? Why does my kernel find this partition and the other
>> one's do not? It's pretty silly to have a backup drive and cannot access it
>> in question ;-)
>
> Which kernel do you boot?
> The systerescue-cd has 4 kernels:
> 2 * 64bit and 2 * 32bit.
>
> By default, it boots the "default" one for the architecture you are booting.
> Have you tried booting the "alternate" kernel?
>
> I have 1 system that I need to boot using the "alternate" kernel as the
> "default" one is too old. (Yes, by default it boots an old kernel)
>
> It could easily be that the kernel you are using does not support your USB3
> adapter or something else you used.
>
> Eg. apart from all the 'ls' statements, also check "uname" and
> "/proc/config.gz" for differences.

I was just reading about "IOMMU" and how often, if it is not "correctly 
configured" in the kernel and other places, your memory map to other 
hardwawre, like USB, can be flaky or not work at all. Fixes often 
require loading the latest bios for your motherboard. It also matters 
the 'rev' of your motherboard and other details.

I have a Gigabyte GA-990FXA-ud3 that seems to be a victim of this bug. 
No, I have not had time to ferret out this issue, so here are a few raw 
links where it is talked about::

https://www.reddit.com/r/linux/comments/4ixnyg/question_about_iommu/

https://en.wikipedia.org/wiki/Input–output_memory_management_unit

http://developer.amd.com/community/blog/2008/09/01/iommu/

http://pages.cs.wisc.edu/~basu/isca_iommu_tutorial/

https://en.wikipedia.org/wiki/List_of_IOMMU-supporting_hardware


(more posted if you ask)...


hth,
James