Re: [PATCH] docs: Update for stopping small mbr gap support

[Daniel Kiper]

On Thu, Mar 05, 2020 at 06:40:01PM +0800, Michael Chang wrote:
> Further to the discussion about disabling btrfs zstd support for
> i386-pc[1], this paragraph in manual about mbr gap size doesn't seem to
> hold true any longer.
>
> "You must ensure that the first partition starts at least 31 KiB (63
> sectors) from the start of the disk"
>
> As in many occasions we inevitablely have to provide core image size
> that goes beyond 31 KiB, this statement becomes a true liability as
> people would be misguided and think it is still fine to use small MBR
> gap, that has always been a headache in distribution's upgrade path as
> growing new feature would render the size requirement bigger but no way
> for the user to relocate their partitions.

Could you split this paragraph into a few sentences? Now it does not
read very well...

> The patch tries to correct the paragraph with a more practical size that
> works for grub and also for modern computer systems in general.
>
> [1] https://lists.gnu.org/archive/html/grub-devel/2019-11/msg00025.html
>
> Signed-off-by: Michael Chang <address@hidden>
> ---
>  docs/grub.texi | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/docs/grub.texi b/docs/grub.texi
> index 83979af38..651468268 100644
> --- a/docs/grub.texi
> +++ b/docs/grub.texi
> @@ -845,12 +845,20 @@ only be used if the @file{/boot} filesystem is on the 
> same disk that the
>  BIOS boots from, so that GRUB does not have to rely on guessing BIOS drive
>  numbers.
>
> -The GRUB development team generally recommends embedding GRUB before the
> -first partition, unless you have special requirements.  You must ensure that
> -the first partition starts at least 31 KiB (63 sectors) from the start of
> -the disk; on modern disks, it is often a performance advantage to align
> -partitions on larger boundaries anyway, so the first partition might start 1
> -MiB from the start of the disk.
> +The GRUB development team generally recommends embedding GRUB before the 
> first
> +partition, unless you have special requirements. You must ensure that the 
> first
> +partition starts at least 1 MiB from the start of the disk; on modern disks, 
> it

s/; on modern disks, it/. Additionally, on modern disks it/

> +is often a performance advantage to align partitions on larger boundaries 
> and 1
> +MiB is the least common multiple of many used alignment sizes. For SSD, it

s/For SSD, it/E.g. SSD, it/

> +became crucial to have the partition correctly aligned to avoid excessive
> +read-modify-write cycles and thus modern tools set to use 1 MiB as a stardard
> +practice.
> +
> +In case legacy systems that cannot boot if first partition not on the 
> cylinder

s/In case legacy/In case of legacy/
s/partition not/partition is not/

> +boundary, the fallback blocklist install method should remain working for 
> them
> +if the core image growing too much someday. Here we just can't advertise that
> +31 KiB (63 sectors) is a sensible size any longer as that would pose great
> +constraint to include new features as time goes by.

Daniel