raid1 or raid10 for /boot

raid1 or raid10 for /boot

[Keld Jørn Simonsen]

I understand that lilo and grub only can boot partitions that look like
a normal single-drive partition. And then I understand that a plain
raid10 has a layout which is equivalent to raid1. Can such a raid10
partition be used with grub or lilo for booting?
And would there be any advantages in this, for example better disk
utilization in the raid10 driver compared with raid?

best regards
keld

Re: raid1 or raid10 for /boot

[Robin Hill]

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On Mon Feb 04, 2008 at 07:34:54AM +0100, Keld Jørn Simonsen wrote:

> I understand that lilo and grub only can boot partitions that look like
> a normal single-drive partition. And then I understand that a plain
> raid10 has a layout which is equivalent to raid1. Can such a raid10
> partition be used with grub or lilo for booting?
> And would there be any advantages in this, for example better disk
> utilization in the raid10 driver compared with raid?
> 
A plain RAID-10 does _not_ have a layout equivalent to RAID-1 and
_cannot_ be used for booting (well, possibly a 2-disk RAID-10 could -
I'm not sure how that'd be layed out).  RAID-10 uses striping as well as
mirroring, and the striping breaks both grub and lilo (and, AFAIK, every
other boot manager currently out there).

Cheers,
        Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: raid1 or raid10 for /boot

[Keld Jørn Simonsen]

On Mon, Feb 04, 2008 at 09:17:35AM +0000, Robin Hill wrote:
> On Mon Feb 04, 2008 at 07:34:54AM +0100, Keld Jørn Simonsen wrote:
> 
> > I understand that lilo and grub only can boot partitions that look like
> > a normal single-drive partition. And then I understand that a plain
> > raid10 has a layout which is equivalent to raid1. Can such a raid10
> > partition be used with grub or lilo for booting?
> > And would there be any advantages in this, for example better disk
> > utilization in the raid10 driver compared with raid?
> > 
> A plain RAID-10 does _not_ have a layout equivalent to RAID-1 and
> _cannot_ be used for booting (well, possibly a 2-disk RAID-10 could -
> I'm not sure how that'd be layed out).  RAID-10 uses striping as well as
> mirroring, and the striping breaks both grub and lilo (and, AFAIK, every
> other boot manager currently out there).

Yes, it is understood that raid10,f2 uses striping, but a raid10,near=2,
far=1 does not use striping, anfd this is what you get if you just make
a    mdadm --create /dev/md0 -l 10 -n 2 /dev/sda1 /dev/sdb1

best regards
keld
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Re: raid1 or raid10 for /boot

[Robin Hill]

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On Mon Feb 04, 2008 at 12:21:40PM +0100, Keld Jørn Simonsen wrote:

> On Mon, Feb 04, 2008 at 09:17:35AM +0000, Robin Hill wrote:
> > On Mon Feb 04, 2008 at 07:34:54AM +0100, Keld Jørn Simonsen wrote:
> > 
> > > I understand that lilo and grub only can boot partitions that look like
> > > a normal single-drive partition. And then I understand that a plain
> > > raid10 has a layout which is equivalent to raid1. Can such a raid10
> > > partition be used with grub or lilo for booting?
> > > And would there be any advantages in this, for example better disk
> > > utilization in the raid10 driver compared with raid?
> > > 
> > A plain RAID-10 does _not_ have a layout equivalent to RAID-1 and
> > _cannot_ be used for booting (well, possibly a 2-disk RAID-10 could -
> > I'm not sure how that'd be layed out).  RAID-10 uses striping as well as
> > mirroring, and the striping breaks both grub and lilo (and, AFAIK, every
> > other boot manager currently out there).
> 
> Yes, it is understood that raid10,f2 uses striping, but a raid10,near=2,
> far=1 does not use striping, anfd this is what you get if you just make
> a    mdadm --create /dev/md0 -l 10 -n 2 /dev/sda1 /dev/sdb1
> 
Well yes, if you do a two-disk RAID-10 then (as I said above) you
probably end up with a RAID-1 (as you do with a two-disk RAID-5).  I
don't see how this would work any differently (or better) than a RAID-1
though (and only serves to confuse things).

If you have more than two disks then RAID-10 will _always_ stripe (no
matter whether you use near, far or offset layout - these affect only
where the mirrored chunks are put) and grub/lilo will fail to work.

Cheers,
        Robin

-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: raid1 or raid10 for /boot

[Bill Davidsen]

Keld Jørn Simonsen wrote:
> I understand that lilo and grub only can boot partitions that look like
> a normal single-drive partition. And then I understand that a plain
> raid10 has a layout which is equivalent to raid1. Can such a raid10
> partition be used with grub or lilo for booting?
> And would there be any advantages in this, for example better disk
> utilization in the raid10 driver compared with raid?
>   

I don't know about you, but my /boot goes with zero use between boots, 
efficiency and performance improvements strike as a distinction without 
a difference, while adding complexity without benefit is always a bad idea.

I suggest that you avoid having a "learning experience" and stick with 
raid1.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 



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Re: raid1 or raid10 for /boot

[Keld Jørn Simonsen]

On Wed, Feb 06, 2008 at 01:52:11PM -0500, Bill Davidsen wrote:
> Keld Jørn Simonsen wrote:
> >I understand that lilo and grub only can boot partitions that look like
> >a normal single-drive partition. And then I understand that a plain
> >raid10 has a layout which is equivalent to raid1. Can such a raid10
> >partition be used with grub or lilo for booting?
> >And would there be any advantages in this, for example better disk
> >utilization in the raid10 driver compared with raid?
> >  
> 
> I don't know about you, but my /boot goes with zero use between boots, 
> efficiency and performance improvements strike as a distinction without 
> a difference, while adding complexity without benefit is always a bad idea.
> 
> I suggest that you avoid having a "learning experience" and stick with 
> raid1.

I agree with you, it was only a theoretical question.

Best regards
keld
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