Re: [PATCH 00/18] Assorted md patches headed for 2.6.30

["Keld Jørn Simonsen" <keld@dkuug.dk>]

On Thu, Feb 12, 2009 at 09:52:32PM +1100, NeilBrown wrote:
> On Thu, February 12, 2009 8:46 pm, Keld Jørn Simonsen wrote:
> > On Thu, Feb 12, 2009 at 09:13:17AM +0000, Steve Fairbairn wrote:
> >> Keld Jørn Simonsen wrote:
> >> >
> >> >I would rather have functionality to convert raid10 to raid5.
> >> >raid1 should be depreciated, as raid10,n2 for all purposes is the same
> >> >but better implementation and performance, and raid10,f2 and raid10,o2
> >> >are even better.  Nobody should use raid1 anymore.
> >> >
> >> Complete ignorance of raid10 here, but is raid10,<anything> bootable,
> >> like raid1 is?  I use raid1 on my root and boot partitions.
> >
> > AFAIK, raid10,n2 in default mode (superblock etc) is bootable, as it
> > looks like two copies of a normal FS. I think this was even reported
> > on this list at some time.
> >
> > You are not the only one that does not know much about raid10. I think
> > most Linux administrators don't.  And other system adminstrators most
> > likely don't either.
> >
> > Maybe we should rename raid10 to raid1?
> >
> > Raid10 should just be an enhanced raid1. And I understand from Neil that
> > raid10,o2 is mostly done because it is a standard raid1 layout. So it is
> > strange that it is not available with raid1 in Linux. And I also think
> > that the raid10,f2 layout is available from some HW raid controllers, as
> > their implementation of raid1. So all what is in raid10 is other places
> > considered raid1 stuff.
> >
> 
> The 'offset' layout came about to be able to support a DDF format
> which is called:
> 
> 4.2.18 Integrated Offset Stripe Mirroring (PRL=11, RLQ=01)
> 
> (4.2.18 is the section of the document
>  PRL is Primary Raid Level
>  RLQ is Rail Level Qualifier
> )
> There is also
> 
> 4.2.17 Integrated Adjacent Stripe Mirroring (PRL= 11, RLQ=00)
> 
> which is essentially the same as our n2 layout.
> 
> You should see their
> 4.3.4 Spanned Secondary RAID Level (SRL=03)
> 
> Though.  That would be really .. interesting to implement.
> 
> 
> You can down load the ddf spec at
> 
> http://www.snia.org/tech_activities/standards/curr_standards/ddf/
> 
> NeilBrown

I did look at the spec, and I could not find something that looked like
f2. I then sent them a mail suggesting standardizing raid10,f2 - some
months ago. No answer (yet...) Am I right that raid10,f2 is not
described in their spec? A bit odd. The idea behind raid10,f2 is quite
straightforward, and gives good results.

Best regards
keld
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