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Re: Current Grub2 & problem with /boot on different drive

From: Dean Loros
Subject: Re: Current Grub2 & problem with /boot on different drive
Date: Mon, 21 Sep 2009 07:10:45 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20090920 Shredder/3.0pre

Today's Topics:
>    7. Re: Current Grub2 & problem with /boot on different drive
>       (Vladimir 'phcoder' Serbinenko)
> ----------------------------------------------------------------------

Message: 7
Date: Sun, 20 Sep 2009 22:00:13 +0200
From: Vladimir 'phcoder' Serbinenko <address@hidden>
Subject: Re: Current Grub2 & problem with /boot on different drive
To: The development of GRUB 2 <address@hidden>
Message-ID: <address@hidden>
Content-Type: text/plain; charset=UTF-8

Dean Loros wrote:

> > Greetings--
> >
> > Ubuntu has been testing Grub2 for a number of months now & a
> > "interesting" problem has surfaced. If your /boot is on a different
> > drive than the MBR, you will have several minutes of drive use before
> > you get to the Grub2 menu. My current timing is 3min 50sec to menu--this
> > is with a i7-920 system with four internal drives--all SATA-II. My first
> > bug report on Launchpad was dated 8-28-2009 & this had started a few
> > days earlier. Before that date, Grub2 would take only 3~5 seconds to get
> > to menu. Updates after this have not cured this issue. The current
> > "work-around" in the bug report is to re-set MBR & /boot to the first
> > drive. This problem only shows up in multi-boot/multi-drive systems.
> >
> >   
We have theoretically discussed this problem with Robert but weren't
sure if instances of it exist. The problem is that (UUID=..) syntax
rescans all drives on every access. We devised a solution to split
search.mod into search_uuid.mod, search_file.mod and so on but we agreed
that it will be done after 1.97 due to amount of changes it requires.
I'm ok to implement it, it's not much work but I can't make any promises
about my current disponibility.
As a workaround for time being you can use one or more of the following:
1) Increase cache size. Can this be done in 1.97?
Change include/grub/disk.h and replace
#define GRUB_DISK_CACHE_NUM     1021
with a bigger number
2) Modify scripts to hardcode boot device and not use UUID. If you
change disk order it will result in boot failure but it may be a local
3) add search -s -u <UUID> as first command of your grub.cfg

Hi Vladimir--

I have tried option #3 & have a question about syntax--should it be just search 
-s -u UUID number or should the number be in <> ?

I tried without the <> & grub took the same ammount of time as before--I have 
edited grub.cfg with the <>, but have not rebooted with it in that form until I 
hear from you on this.

Dean Loros

Dean Loros
autocrosser at
Performance by Design Ltd.

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