Re: md extension to support booting from raid whole disks.

[Peter Rabbitson <rabbit+list@rabbit.us>]

Goswin von Brederlow wrote:
> Micha³ Przy³uski <mikylie@gmail.com> writes:
> 
> 
> The point was not to add redundancy but to remove complexity.
> 
> Just look at what you need to do for the next generation of disks
> (>2TB):
> 
> - Create a MS Dos partition table with a fake /boot partition in the
>   first 2TB.
> - Create a GPT table with a matching /boot partition and the rest
> - Create a raid1 for /boot
> - Create a raidX for the rest
> 
> Now you have to watch 2 raids and add/remove partitions from 2 raids,
> You also need to copy the bootloader to every new disk you add.
> 
> The idea is to bring this down to:
> 
> - Create raidX over all disks
> 
>> it a hidden raid1 over first few sectors is just creating an
>> automation that gains nothing and makes things unnecessarily
>> complicated inside.
> 
> If the hidden raid1 is just reserved space that is considered part of
> the raid metadata then this moves completly into mdadm userspace. The
> extra complexity comes down to "read reserved space from old disk,
> write reserved space to new disk". In the most basic form that is 3
> lines of code (declare buffer, read, write).
> 

This is the best description of the problem/benefit so far. Also when
deciding on the size of the reserved space, factor in possible
bitmap size explosion when moving from say a 4x300G raid6 to a 4x2T raid6.

+1 on this feature request

Cheers
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