Re: [RFC] grub-install C rewrite - Vladimir 'φ-coder/phcoder' Serbinenko

From: "Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>
To: The development of GNU GRUB <grub-devel@gnu.org>
Subject: Re: [RFC] grub-install C rewrite
Date: Fri, 27 Sep 2013 00:15:24 +0200	[thread overview]
Message-ID: <5244B1FC.9050503@gmail.com> (raw)
In-Reply-To: <4A8339E2-1CD6-446C-96BC-8733A5C8D552@colorremedies.com>

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On 26.09.2013 22:51, Chris Murphy wrote:
> 
> On Sep 26, 2013, at 2:22 PM, Lennart Sorensen <lsorense@csclub.uwaterloo.ca> wrote:
> 
>> On Thu, Sep 26, 2013 at 08:49:52PM +0200, Vladimir 'φ-coder/phcoder' Serbinenko wrote:
>>> This is interesting testcase which wasn't brought before. This would
>>> potentially involve creating several core.img or forcing UUID when using
>>> multiple devices. Again, pretty easy in C and hairy in bash due to list
>>> handling.
>>
>> No, one core.img is fine.  The boot disk is the boot disk in each case
>> (so on x86 device 0x80).  The same core.img gets inserted too all the
>> devices, so that if it happens to be the boot disk, it works.  Since the
>> partition is raid1, the same UUID is everywhere.  I do not expect
>> booting from a raid5 device to be possible as the boot partition (althoug
>> hperhaps grub is smart enough to read the kernel from an md raid5 device
>> these days).
> 
> It is. Even raid6 is possible. The limitation is the BIOS being able to present all member devices to grub for it to assemble the raid in order to find /boot. But I don't know if it can work on a degraded array by rebuilding parity. If not, I see no point in /boot on raid5/6.
> 
> The case of btrfs raid0/1/10 is interesting. It's possible to boot all of these with GRUB2, I've tried up to 4 disks for those raid levels, and includes support for subvolumes/snapshots. I haven't extensively tried to break it with many snapshots, deletions, etc. So I don't know how resilient it is. The ability to boot raid1/10 with a missing member is useful. And it's actually a more complex setup to incorporate md raid and ext4 on those same disks for a separate /boot; or possibly losing ability to boot if /boot is on a single disk, which also complicates the layout. For such a layout, core.img is needed for each disk.
> 
> Open question is if on BIOS hardware, if a 1MB BIOSBoot is preferred over the 64KB Btrfs bootloader pad? I don't know off hand if each member disk, or subsequently added disks, each have this 64KB pad or just the first member.
> 
This is besides the point. I'm fine to discuss such things but in a
separate thread.
> 
> Chris Murphy
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> Grub-devel@gnu.org
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> 


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