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List:       linux-raid
Subject:    Re: RAID1 root and swap and initrd
From:       Bill Davidsen <davidsen () tmr ! com>
Date:       2006-12-21 18:47:35
Message-ID: 458AD6C7.80405 () tmr ! com
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Michael Tokarev wrote:
> [A late follow-up]
>
> Bill Davidsen wrote:
>   
>> Michael Tokarev wrote:
>>     
>>> Andre Majorel wrote:
>>> []
>>>  
>>>       
>>>> Thanks Jurriaan and Gordon. I think I may still be f*cked,
>>>> however. The Lilo doc says you can't use raid-extra-boot=mbr-only
>>>> if boot= does not point to a raid device. Which it doesn't because
>>>> in my setup, boot=/dev/sda.
>>>>
>>>> Using boot=/dev/md5 would solve the raid-extra-boot issue but the
>>>> components of /dev/md5 are not primary partitions (/dev/sda5,
>>>> /dev/sdb5) so I don't think that would work.
>>>>         
>>> So just move it to sda1 (or sda2, sda3) from sda5, ensure you've
>>> two identical drives (or at least your boot partitions are layed
>>> up identically), and use boot=/dev/md1 (or md2, md3).  Do NOT
>>> use raid-extra-boot (set it to "none"), but set up standard mbr
>>> code into boot sector of both drives (in debian, it's 'mbr' package;
>>> lilo can be used for that too - once for each drive), and mark your
>>> boot partition on both drives as active.
>>>
>>> This is the most clean setup to boot off raid.  You'll have two
>>> drives, both will be bootable, and both will be updated when
>>> you'll run lilo.
>>>
>>> Another bonus - if you'll ever install a foreign OS on this system,
>>> which tends to update boot code, all your stuff will still be intact -
>>> the only thing you'll need to do to restore linux boot is to reset
>>> 'active' flags for your partitions (and no, winnt disk manager does
>>> not allow you to do so - no ability to set non-dos (non-windows)
>>> partition active).
>>>
>>>       
>>>> I *could* run lilo once for each disk after tweaking boot= in
>>>> lilo.conf, or just supply a different -M option but I'm not sure.
>>>> The Lilo doc is not terribly enlightening. Not for me, anyway. :-)
>>>>         
>>> No, don't do that. Even if you can automate it.  It's error-prone
>>> to say the best, and it will bite you at an unexpected moment.
>>>       
>> The desirable solution is to use the DOS MBR (boot active partition) and
>> put the boot stuff in the RAID device. However, you can just write the
>> MBR to the hda and then to hdb. Note that you don't play with the
>> partition names, the 2nd MBR will only be used if the 1st drive fails,
>> and therefore at the BIOS level the 2nd drive will now be hda (or C:) if
>> LILO stiff uses the BIOS to load the next sector.
>>     
>
> Just a small note.  DOS MBR can't boot from non-primary partition.
> In this case, the boot code is at sda5, which is on extended partition.
>
> But.  Lilo now has ability to write its own MBR, which, in turn, IS
> able to boot of logical partition.
>
>  lilo -M /dev/sda ext
>
>   

Useful if you can't use a primary for /boot for some reason. grub can do 
this as well, of course.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

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