grub and mdadm

grub and mdadm

[AdsGroup]

In the past I have used whole drives (<2TB) as block devices for mdadm 
raid and a separate single drive for grub, boot, swap, root and home 
with no problem. I now want to upgrade (non-UEFI bios machine) to 
multiple 3TB drives thinking 3 active in Raid 5 with 1 spare again using 
the full drives as block devices and installing Lubuntu 12.10 LTS 
alternate for server/command line.

Using Lubuntu 13.10 desktop live (therefore recent mdadm, gparted, 
parted, etc) I've created and easily assembled/started the mdadm array 
/dev/md0 from sd[a-c], sdd as spare. I then partition /dev/md0 on MIB 
boundaries the following in order 1MB free space, 2MB bios-grub, 200MB 
boot, 10GB swap, remainder root (5.6 TB?) with 1MB trailing free space.

Then rebooting to 12.10 alternate for install I have difficulties 
installing grub anywhere. Even fails using boot-repair (link below) Any 
ideas?

Ashley



https://help.ubuntu.com/community/Boot-Repair

Re: grub and mdadm

[Chris Murphy]

On Mar 9, 2014, at 6:24 PM, AdsGroup <AdsGroup@shaw.ca> wrote:

> In the past I have used whole drives (<2TB) as block devices for mdadm raid and a separate single drive for grub, boot, swap, root and home with no problem. I now want to upgrade (non-UEFI bios machine) to multiple 3TB drives thinking 3 active in Raid 5 with 1 spare again using the full drives as block devices and installing Lubuntu 12.10 LTS alternate for server/command line.
> 
> Using Lubuntu 13.10 desktop live (therefore recent mdadm, gparted, parted, etc) I've created and easily assembled/started the mdadm array /dev/md0 from sd[a-c], sdd as spare. I then partition /dev/md0 on MIB boundaries the following in order 1MB free space, 2MB bios-grub, 200MB boot, 10GB swap, remainder root (5.6 TB?) with 1MB trailing free space.

The disks should be partitioned first, so that each disk has a completely whole BIOS boot, with a complete GRUB core.img. The only reason why this worked is probably a bit of luck that grub-install of core.img put it in a single chunk that just so happened to be on the same disk with the initial bootsstrap code. But this setup isn't bootable degraded, like it could be if the layout were minimally partitioned first so that BIOS boot is outside of the array.

> 
> Then rebooting to 12.10 alternate for install I have difficulties installing grub anywhere. Even fails using boot-repair (link below) Any ideas?


Just use the newer 13.10 GRUB, you don't need a 2nd instance to boot the older distribution. Just write a forwarding entry in the 13.10 grub.cfg, via /etc/grub.d/custom_40, using the configfile command pointing to the 12.10 grub.cfg. 


Chris Murphy

Re: grub and mdadm

[Chris Murphy]

Please reply to the list also.


On Mar 10, 2014, at 4:21 PM, Garboge <garboge@shaw.ca> wrote:

> Thanks Chris, I was not clear in presenting my situation. The machine I'm working on is a different machine starting from scratch.
> 
> I should have asked if there is anyway of installing Lubuntu 12.10 on a block device mdadm raid. I actually get to the point of installing grub. Is what I'm asking possible?

I have no idea, but even if it can be done doesn't mean it should be done. I suspect upstream GRUB would say, BIOS Boot inside md raid isn't supported.

Two GRUBs cannot be embedded on BIOS computers. You can chainload one from the other using the multiboot command, or you can use configfile. Each distribution makes substantial changes to the upstream GRUB package, so ultimately any GRUB question quickly turns into a distro specific GRUB question.


Chris Murphy