Ubuntu mdadm Raid and EFI

Ubuntu mdadm Raid and EFI

[Dominique]

Hi,

After testing mdadm on virtual machines, I bought new hardware, as I 
thought I was ready... Well think again.

My HW setup is as follow:
Asus MB P8H67-I (with a Corei5 CPU)
8 GB Memory
6 x 3 TB WD HDD (AHCI mode in the BIOS)
OS: Ubuntu 11.04 x64 Server

My intended SW setup  is as follow:
md1 /boot on RAID1 6 HDD (250 MB x6)
md2 /swap on RAID1 6 HDD (32 GB x6)
md3 / on RAID5 6 HDD (3 TB x6)

First thing first, I followed the usual setup process, with one 
surprise, the boot flag did not hold in the md1 setup. Not a show 
stopper at this step.
When trying to write the GRUB2 information I got stuck with the 
impossility to write the information.
Obviously I could not boot from the HDD after restart.

I then realized that this MB uses a BIOS EFI.
Since that's pretty new stuff for the PC world (not on the MAC side 
though), I am wondering how to mix EFI with RAID... ?

Any help will be more than welcome.

Dominique

Re: Ubuntu mdadm Raid and EFI

[Dominique]

Ok, nothing like writing a mail to get intuition for the next steps..

First I simplified the initial setup.
RAID1 for everyone, and only two HDD to start. I'll convert and expand 
at a later stage.
I also added an EFI partition ('bootgrup' if I remember well). I did 
that on both disk.
Reboot and voila, it boots.

But this kind of negates the RAID1 /boot logic. If the first disk fail, 
then what ? No EFI, no boot ?
How - if possible - do you configure EFI to boot from RAID1 across xHDD 
to allow boot in degraded mode ?

Dominique

On 24/11/2011 15:09, Dominique wrote:
> Hi,
>
> After testing mdadm on virtual machines, I bought new hardware, as I 
> thought I was ready... Well think again.
>
> My HW setup is as follow:
> Asus MB P8H67-I (with a Corei5 CPU)
> 8 GB Memory
> 6 x 3 TB WD HDD (AHCI mode in the BIOS)
> OS: Ubuntu 11.04 x64 Server
>
> My intended SW setup  is as follow:
> md1 /boot on RAID1 6 HDD (250 MB x6)
> md2 /swap on RAID1 6 HDD (32 GB x6)
> md3 / on RAID5 6 HDD (3 TB x6)
>
> First thing first, I followed the usual setup process, with one 
> surprise, the boot flag did not hold in the md1 setup. Not a show 
> stopper at this step.
> When trying to write the GRUB2 information I got stuck with the 
> impossility to write the information.
> Obviously I could not boot from the HDD after restart.
>
> I then realized that this MB uses a BIOS EFI.
> Since that's pretty new stuff for the PC world (not on the MAC side 
> though), I am wondering how to mix EFI with RAID... ?
>
> Any help will be more than welcome.
>
> Dominique
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>

Re: Ubuntu mdadm Raid and EFI

[Jes Sorensen]

On 11/24/11 17:11, Dominique wrote:
> Ok, nothing like writing a mail to get intuition for the next steps..
> 
> First I simplified the initial setup.
> RAID1 for everyone, and only two HDD to start. I'll convert and expand
> at a later stage.
> I also added an EFI partition ('bootgrup' if I remember well). I did
> that on both disk.
> Reboot and voila, it boots.
> 
> But this kind of negates the RAID1 /boot logic. If the first disk fail,
> then what ? No EFI, no boot ?
> How - if possible - do you configure EFI to boot from RAID1 across xHDD
> to allow boot in degraded mode ?

Depends on how you create your raid - if you use IMSM raid, you can put
the EFI partition on the raid1 device as well. Given you have a
motherboard with an i5 processor, I would expect it to have support for
IMSM raid.

Check the BIOS settings for the drives - if you flip them from AHCI to
raid mode you ought to be able to do it this way.

Cheers,
Jes

Re: Ubuntu mdadm Raid and EFI

[John Robinson]

On 24/11/2011 16:11, Dominique wrote:
> Ok, nothing like writing a mail to get intuition for the next steps..
>
> First I simplified the initial setup.
> RAID1 for everyone, and only two HDD to start. I'll convert and expand
> at a later stage.
> I also added an EFI partition ('bootgrup' if I remember well). I did
> that on both disk.
> Reboot and voila, it boots.
>
> But this kind of negates the RAID1 /boot logic. If the first disk fail,
> then what ? No EFI, no boot ?
> How - if possible - do you configure EFI to boot from RAID1 across xHDD
> to allow boot in degraded mode ?

I haven't used EFI/GPT at all yet, but I imagine the same as the 
old-fashioned MBR technique: install the boot loader separately on all 
the devices you might need to boot from. The CentOS and Fedora 
installers automatically do this for you with MBR and presumably with 
GPT as well if you configure /boot to be a md RAID-1 i.e. they put grub 
on all the drives making up /boot, and I would have thought the Ubuntu 
installer would as well, but you can do it by hand if you have to. Just 
replicate whatever's on sda to sdb, sdc etc.

Then when your first hard disc fails and you reboot, the BIOS will boot 
the first hard disc it finds, which will be your second hard disc, and 
all will be lovely. This doesn't work if your first hard disc is still 
visible but unreadable, but that's always been the problem, and you need 
BIOS RAID support (e.g. Intel IMSM) to cope with it.

And a quick suggestion: use RAID 10 for your swap partition, it'll be 
faster than RAID 1. Since you want to be able to survive 2 disc 
failures, you probably ought to use layout raid10,f3.

Hope this helps.

Cheers,

John.

-- 
John Robinson, yuiop IT services
0131 557 9577 / 07771 784 058
46/12 Broughton Road, Edinburgh EH7 4EE