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

[Michael Chang]

On Thu, Mar 05, 2020 at 03:38:20PM +0100, Daniel Kiper wrote:
> 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...

OK. I'll come up with a better expression next version.

> 
> > 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/

OK.

> 
> > +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/

OK.

> 
> > +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/

OK.

> 
> > +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.

Thanks a lot for taking time to review.

Regards,
Michael

> 
> Daniel
> 
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