[Solved] software raid on new install of LM14 won't boot.

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[Solved] software raid on new install of LM14 won't boot.

Postby skatastic on Sat Dec 15, 2012 3:41 pm

I wanted to install LM14 with softraid0. (I accept risk of data loss). I found several guides on forums around the net which to some degree contradicted each other so I had to use my intuition a bit to decide what to do.
System specs:
Asus p9x79 mobo
intel i7 3820
2 ssd ata corsair neutron
32gb of ram

Here's what I did:
1. For both disks create 3 partitions (1. 100mb ext4, 2. 20gb linux-swap, 3. the rest unformatted)
2. used mdadm to combine sd[ab]3 into /dev/md0
3. ran LM14 installer and chose 'other' for where to install
4. picked sda1 as /boot
5. picked md0 as /
6. pointed grub to sda

I had previously done the above without the 100mb /boot partition which caused the install to fail at grub installation, which is why I chose to use a non-raid partition for /boot. This time, It seemed as if everything was going to work because install didn't throw any errors and finished with success.

When I tried to boot, the grub menu appears but booting fails with
Code: Select all
Gave up waiting for root device.

followed by a few lines of common problems then
Code: Select all
ALERT! /dev/md0 does not exist.  Dropping to a shell


When I boot into live cd and open Gparted it first says that it can't find /dev/md0 but then /md127pl shows up instead. At this point I'm unable to access the files within the raid but if i download mdadm again I can access and see the installation of LM14. At this point I thought well maybe if I point grub to md127 instead of md0 then it would work so I went into grub.cfg and changed md0 to md127 in the two lines of root=...
I still got the same error as above except this time it said md127 doesn't exist. On the next boot into the LiveCD when I open Gparted it doesn't give me the error about not finding md0 and instead just shows md127. I still couldn't see the files on that partition until reinstalling mdadm.
It seems as though the problem is that my /boot partition doesn't have mdadm so grub doesn't know how to see the raided partition. Is this assumption correct? How do I resolve it?
Last edited by skatastic on Mon Dec 17, 2012 8:32 pm, edited 1 time in total.
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Re: software raid on new install of LM14 won't boot.

Postby mintybits on Sat Dec 15, 2012 5:04 pm

You don't need a separate boot partition. 20GB for swap is a huge overkill. 4GB total swap usually more than enough.
The thing is, the Mint installer is not designed to install to a RAID device and so you have to do quite a few things to make it work.

1) When you boot the live CD you first have to install mdadm
2) You then need to create or assemble the RAID device
3) Then run the installer. It will fail at Grub install.
4) You then need to Chroot into the RAID root and install mdadm again, edit mdadm.conf, edit fstab, run update-initramfs -u and dpkg-reconfigure grub-pc.

It's a bit of a faff.
Chrooting: https://help.ubuntu.com/community/Grub2 ... via_ChRoot
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Re: software raid on new install of LM14 won't boot.

Postby skatastic on Sat Dec 15, 2012 7:01 pm

I'll give that a try next time I have some time to burn. As far as the swap partition goes I was thinking of the old rule of 2x physical memory but after a quick search I see that I have been living in the stone age.
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Re: software raid on new install of LM14 won't boot.

Postby skatastic on Mon Dec 17, 2012 8:31 pm

I finally got it working. I was having trouble getting it to work with the instructions as given but after I did the purge/reinstall it did work. I did the other steps again too so chances are equally good that I did one of those incorrectly the first time but either way, it works now!
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Re: [Solved] software raid on new install of LM14 won't boot

Postby bdensmore on Wed Dec 19, 2012 2:32 am

skatastic, could you take a look at this guide and tell me what you did differently?

http://superuser.com/questions/323339/h ... nt-live-cd

Everything works great until I get to step 5 and try to chroot. Once I do chroot and try to reinstall mdadm I am getting errors trying to download from archive.ubuntu.com. I'm not sure why though. I can ping archive.ubuntu.com and ping any other domain so I know it's not a DNS error or internet connection on my part.

Thank you
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Re: [Solved] software raid on new install of LM14 won't boot

Postby dcsun on Sat Feb 02, 2013 9:31 pm

@bdensmore, you've probably moved on as this is 6 weeks later, but I came across this post in my attempts to get Mint 14 Cinnamon running on RAID1. The cause of that error connecting to the package server is because the /etc/resolv.conf file gets emptied of its DNS servers at some point in the installation process. You can either rebuild that with something from your ISP, or I copied a version I found elsewhere: "cp /etc/resolvconf/resolv.conf.d/tail /etc/resolv.conf". That fixed the error and I was able to install MDADM again and continue on.

That said, I still couldn't make it work after many, many, many hours of playing with several different tutorials I found, as well as combining them, and trying other things on my own. The RAID part seems to be perfect (and I did learn a ton about software RAID and Linux itself through this process, so it wasn't totally wasted), but I could never get the boot loader part to work. I'd either get a black screen with just "GRUB" and a flashing cursor, or a blank screen entirely, even though the GRUB installation process seemed to go okay. If anyone has any light to shed on this I'd appreciate hearing from you, as I'd still like to try get this working at some point. I gave up and went to a single hard disk and I'll just do an RSync or something to the second drive, it's just my desktop workstation, but I really expected to be able to get this working. Single disk installation worked perfectly and was up and running in under 15 minutes.

Dave
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