Re: Problem with grub-install (d-i, soft RAID6, Jessie)

[Pascal Hambourg <pascal@plouf.fr.eu.org>]

Christian Seiler a écrit :
> On 01/08/2016 02:51 AM, Pascal Hambourg wrote:
>> Current tools won't align for compatibility purpose any more. The
>> default 1-MiB alignment is only for performance purpose, not compatibility.
> 
> This is new to me - I always thought that this was entirely for
> compatibility. I'm curious: How would that help performance-wise?
> On SSDs it shouldn't matter at all - and if you have rotational
> media, you'd need to figure out the physical (not the logical)
> geometry of the drive to be effective - and if I'm not mistaken
> there's no standardized way of getting to that via software. What
> am I missing here?

The real physical geometry does not matter at all. What matters is only
the physical read/write/erase block size. You get a read-modify-write
penalty if you don't align write operations on proper block boundaries.
1 MiB was chosen as a multiple of all common block sizes for both SSD
and 512e "Advanced  Format" hard disks.

See for example
<https://en.wikipedia.org/wiki/Solid-state_drive#File_systems_suitable_for_SSDs>
<https://en.wikipedia.org/wiki/Advanced_Format#512e>