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.
>
>
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--
Regards,
Heinz -- The LVM Guy --
*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
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Heinz Mauelshagen Red Hat GmbH
Consulting Development Engineer Am Sonnenhang 11
Cluster and Storage Development 56242 Marienrachdorf
Germany
[email protected] +49 2626 141200
FAX 924446
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