From: Heinz Mauelshagen <mauelshagen@redhat.com>
To: Phillip Susi <psusi@cfl.rr.com>
Cc: Neil Brown <neilb@suse.de>,
Jan Engelhardt <jengelh@linux01.gwdg.de>,
"Lincoln Dale (ltd)" <ltd@cisco.com>,
Michael Tokarev <mjt@tls.msk.ru>,
linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
"Steinar H. Gunderson" <sgunderson@bigfoot.com>
Subject: Re: [PATCH 000 of 5] md: Introduction
Date: Fri, 20 Jan 2006 19:41:25 +0100 [thread overview]
Message-ID: <20060120184125.GC2799@redhat.com> (raw)
In-Reply-To: <43D04828.8010107@cfl.rr.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.
>
>
> -
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--
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
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next prev parent reply other threads:[~2006-01-20 18:41 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-17 21:38 [PATCH 000 of 5] md: Introduction Lincoln Dale (ltd)
2006-01-18 13:27 ` Jan Engelhardt
2006-01-18 23:19 ` Neil Brown
2006-01-19 15:33 ` Mark Hahn
2006-01-19 20:12 ` Jan Engelhardt
2006-01-19 21:22 ` Lars Marowsky-Bree
2006-01-19 22:17 ` Phillip Susi
2006-01-19 22:32 ` Neil Brown
2006-01-19 23:26 ` Phillip Susi
2006-01-19 23:43 ` Neil Brown
2006-01-20 2:17 ` Phillip Susi
2006-01-20 10:53 ` Lars Marowsky-Bree
2006-01-20 12:06 ` Jens Axboe
2006-01-20 18:38 ` Heinz Mauelshagen
2006-01-20 22:09 ` Lars Marowsky-Bree
2006-01-21 0:06 ` Heinz Mauelshagen
2006-01-20 18:41 ` Heinz Mauelshagen [this message]
2006-01-20 17:29 ` Ross Vandegrift
2006-01-20 18:36 ` Heinz Mauelshagen
2006-01-20 22:57 ` Lars Marowsky-Bree
2006-01-21 0:01 ` Heinz Mauelshagen
2006-01-21 0:03 ` Lars Marowsky-Bree
2006-01-21 0:08 ` Heinz Mauelshagen
2006-01-21 0:13 ` Lars Marowsky-Bree
2006-01-23 9:44 ` Heinz Mauelshagen
2006-01-23 10:26 ` Lars Marowsky-Bree
2006-01-23 10:38 ` Heinz Mauelshagen
2006-01-23 10:45 ` Lars Marowsky-Bree
2006-01-23 11:00 ` Heinz Mauelshagen
2006-01-23 12:54 ` Ville Herva
2006-01-23 13:00 ` Steinar H. Gunderson
2006-01-23 13:54 ` Heinz Mauelshagen
2006-01-23 17:33 ` Ville Herva
2006-01-24 2:02 ` Phillip Susi
2006-01-24 7:26 ` Error message for invalid initramfs cpio format? Ville Herva
-- strict thread matches above, loose matches on Subject: below --
2006-01-20 18:05 [PATCH 000 of 5] md: Introduction Hubert Tonneau
2006-01-20 17:01 Hubert Tonneau
2006-01-20 16:15 ` Christoph Hellwig
2006-01-22 6:45 ` Herbert Poetzl
2006-01-20 16:48 Hubert Tonneau
2006-01-17 6:56 NeilBrown
2006-01-17 8:17 ` Michael Tokarev
2006-01-17 9:50 ` Sander
2006-01-17 11:26 ` Michael Tokarev
2006-01-17 14:03 ` Kyle Moffett
2006-01-19 0:28 ` Neil Brown
2006-01-17 16:08 ` Ross Vandegrift
2006-01-17 18:12 ` Michael Tokarev
2006-01-18 8:14 ` Sander
2006-01-18 9:03 ` Alan Cox
2006-01-19 0:22 ` Neil Brown
2006-01-19 9:01 ` Jakob Oestergaard
2006-01-17 22:38 ` Phillip Susi
2006-01-17 22:57 ` Neil Brown
2006-01-17 14:10 ` Steinar H. Gunderson
2006-01-22 4:42 ` Adam Kropelin
2006-01-22 22:52 ` Neil Brown
2006-01-23 23:02 ` Adam Kropelin
2006-01-23 1:08 ` John Hendrikx
2006-01-23 1:25 ` Neil Brown
2006-01-23 1:54 ` Kyle Moffett
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