Re: [PATCH 000 of 5] md: Introduction

[Heinz Mauelshagen <mauelshagen@redhat.com>]

On Thu, Jan 19, 2006 at 09:17:12PM -0500, Phillip Susi wrote:
> Neil Brown wrote:
> 
> >Maybe the problem here is thinking of md and dm as different things.
> >Try just not thinking of them at all.  
> >Think about it like this:
> > The linux kernel support lvm
> > The linux kernel support multipath
> > The linux kernel support snapshots
> > The linux kernel support raid0
> > The linux kernel support raid1
> > The linux kernel support raid5
> >
> >Use the bits that you want, and not the bits that you don't.
> >
> >dm and md are just two different interface styles to various bits of
> >this.  Neither is clearly better than the other, partly because
> >different people have different tastes.
> >
> >Maybe what you really want is for all of these functions to be managed
> >under the one umbrella application.  I think that is was EVMS tried to
> >do. 
> >
> > 
> >
> 
> I am under the impression that dm is simpler/cleaner than md.  That 
> impression very well may be wrong, but if it is simpler, then that's a 
> good thing. 
> 
> 
> >One big selling point that 'dm' has is 'dmraid' - a tool that allows
> >you to use a lot of 'fakeraid' cards.  People would like dmraid to
> >work with raid5 as well, and that is a good goal.
> > 
> >
> 
> AFAIK, the hardware fakeraid solutions on the market don't support raid5 
> anyhow ( at least mine doesn't ), so dmraid won't either. 

Well, some do (eg, Nvidia).

> 
> >However it doesn't mean that dm needs to get it's own raid5
> >implementation or that md/raid5 needs to be merged with dm.
> >It can be achieved by giving md/raid5 the right interfaces so that
> >metadata can be managed from userspace (and I am nearly there).
> >Then 'dmraid' (or a similar tool) can use 'dm' interfaces for some
> >raid levels and 'md' interfaces for others.
> >
> 
> Having two sets of interfaces and retrofiting a new interface onto a 
> system that wasn't designed for it seems likely to bloat the kernel with 
> complex code.  I don't really know if that is the case because I have 
> not studied the code, but that's the impression I get, and if it's 
> right, then I'd say it is better to stick with dm rather than retrofit 
> md.  In either case, it seems overly complex to have to deal with both. 

I agree, but dm will need to mature before it'll be able to substitute md.

> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Red Hat GmbH
Consulting Development Engineer                   Am Sonnenhang 11
Cluster and Storage Development                   56242 Marienrachdorf
                                                  Germany
Mauelshagen@RedHat.com                            +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/