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nelsonwcf
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PostPosted: Tue Aug 30, 2016 1:00 am    Post subject: Finding the correct root partition: Reply with quote

Hi,

I've just finished installing gentoo on my new computer. However, I can't find the correct root partition for booting.
I'm using two SSDs in RAID0 partition as GPT. I'm also using rEFInd. In Gentoo liveCD the partition device becomes /dev/md126p6. However, neither that one nor /dev/sda6 works as the mount point. How can I find the correct boot device for the root partition if when booting using livecds it changes?

Thank you,
Nelson

EDIT: Looking the boot screen, I've noticed that only sda and sdb are being detected in the boot so the system is not mounting the volumes. My RAID0 should be hardware managed. Do I have specific options in the kernel turned on? Shouldn't the kernel sees only the logical drive instead of the two physical drivers?
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Buffoon
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PostPosted: Tue Aug 30, 2016 2:02 am    Post subject: Reply with quote

Kernel sees separate drives? You have no hardware RAID. You have software RAID which can be set up in firmware. RH invented the soft for it, called dmraid. You are much better off using mdraid instead.
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nelsonwcf
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PostPosted: Tue Aug 30, 2016 2:56 am    Post subject: Reply with quote

Buffoon wrote:
Kernel sees separate drives? You have no hardware RAID. You have software RAID which can be set up in firmware. RH invented the soft for it, called dmraid. You are much better off using mdraid instead.


Interesting. I thought that RAIDs that are created in BIOS are considered hardware RAID. Since it's firmware RAID, what would be the best approach?
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Buffoon
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PostPosted: Tue Aug 30, 2016 3:47 am    Post subject: Reply with quote

You decide.
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nelsonwcf
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PostPosted: Tue Aug 30, 2016 1:21 pm    Post subject: Reply with quote

Since I use multi-os environment, I will need to use firmware RAID.
Now, for linux to see the strip volume during boot, what do I have to do? Is it configured the same way as regular software RAID? Is the information in the following link enough or do I have to create an initramfs?

https://wiki.gentoo.org/wiki/Complete_Handbook/Software_RAID

Thank you,
Nelson
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Buffoon
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PostPosted: Tue Aug 30, 2016 1:44 pm    Post subject: Reply with quote

I do not multiboot, so I have no clue. All I know there is dmraid for cases like this.
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PostPosted: Tue Aug 30, 2016 3:23 pm    Post subject: Re: Finding the correct root partition. Reply with quote

nelsoncwf wrote:
I'm using two SSDs in RAID0 partition as GPT. I'm also using rEFInd. In Gentoo liveCD the partition device becomes /dev/md126p6. However, neither that one nor /dev/sda6 works as the mount point. How can I find the correct boot device for the root partition if when booting using livecds it changes?

nelsoncwf wrote:
EDIT: Looking the boot screen, I've noticed that only sda and sdb are being detected in the boot so the system is not mounting the volumes. My RAID0 should be hardware managed. Do I have specific options in the kernel turned on? Shouldn't the kernel sees only the logical drive instead of the two physical drivers?

Why do you say that partitions can't be mounted? How do you know?
Why do you say that devices identifiers change when boot?

Please, be more precise (cf link):
  • tell us what commands executed,
  • describe the symptoms of your problem carefully and clearly,
  • describe the environment in which it occurs,
  • describe the problem's symptom, not your guesses.
  • ...

Please, try to stay cool! 8) (don't be angry! :evil: )

P.S: there are plenty of informations about raid disks in Gentoo forums. The wiki page isn't comprehensive!

Best regards, feng.
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nelsonwcf
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PostPosted: Tue Aug 30, 2016 3:57 pm    Post subject: Reply with quote

My question is more basic than that. I just need to be able to boot in linux.

Since I'm using rEFInd as the bootloader, I have to include the mount point in the kernel config, compile it than place the image in the boot. Right now, it can't find the mount point so it panicks. What device should I use to tell the kernel where the root partition is? /dev/md126p6 is not working. /dev/md/Evo_0p6 is also not working.

Do I have to include some specific kernel options in the config for the kernel to recognize the strip partitions?

Thank you.
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Buffoon
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PostPosted: Tue Aug 30, 2016 4:08 pm    Post subject: Reply with quote

You probably need to build an initrd to assemble and mount it. What is the other OS you are dual booting with? Is it compatible with mdraid (it seems this is what you want to use).
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NeddySeagoon
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PostPosted: Tue Aug 30, 2016 4:57 pm    Post subject: Reply with quote

nelsonwcf,

For fakeraid, you need dm-mapper support in your kernel and the out of kernel dmraid module in your initrd.
With that set up, the init script in the initrd. can assemble your fake raid, then mounting root can proceed.
That's for standard bios fakeraid.

There are other sorts of raid too. Windows has a feature called 'Dynamic Disks'. That's software raid for Windows.
The Linux kernel understands that too.

A few Intel chipsets do something that's a hybrid between fakeraid and software raid.
You set up the raid in the BIOS, then its managed by mdadm in linux.
Windows understands this raid too.
In mdadm its a Container.

Even with fakeraid, the kernel will still see all of the underlying discs.
You will see a few scary errors in dmesg, that you should ignore too.
With fakeraid0, the partition table that describes all the space is on one drive.
dmesg will tell you that the partitions end after the end of the drive.
That's correct it does.
dmesg will tell that one drive is missing a partition table. That's correct too.
Do not attempt do do anything with the individual members of a fakeraid set.

Fakeraid is in general, a very bad thing but its hidden from Windows users, who form most of the market.

Genkernel used to be able to build a working kernel and initrd for fakeraid.
Check the docs but from memory, you need the dmraid option.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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nelsonwcf
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PostPosted: Thu Sep 08, 2016 10:47 pm    Post subject: Reply with quote

Okay, I've tried everything listed in this thread, at least three different gentoo guides (https://forums.gentoo.org/viewtopic-t-888520.html, https://wiki.gentoo.org/wiki/Complete_Handbook/Software_RAID, www.rodsbooks.com/refind/linux.html, https://wiki.gentoo.org/wiki/Gentoo_installation_tips_and_tricks, etc.) and some threads in this forum. I can't seem to make my linux boot because of the RAID 0. Genkernel also doesn't work for me, it doesn't show any problems but after the system reboots it doesn't find the root.

Can someone help me figure out what is happening?

Some information:
- Fake Raid partition;
- rEFInd Bootloader;
- Dual OS (Windows / Linux);
- In Gentoo LiveCD the harddrive shows as md126; the linux partition is 6, thus /dev/md126p6;
- mdadm is emerged;

Any other information needed?

Thank you,
Nelson
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