On Fri, Jan 20, 2006 at 10:43:13AM +1100, Neil Brown wrote: > On Thursday January 19, psusi@xxxxxxxxxx wrote: > > Neil Brown wrote: > > > > > > The in-kernel autodetection in md is purely legacy support as far as I > > > am concerned. md does volume detection in user space via 'mdadm'. > > > > > > What other "things like" were you thinking of. > > > > > > > Oh, I suppose that's true. Well, another thing is your new mods to > > support on the fly reshaping, which dm could do from user space. Then > > of course, there's multipath and snapshots and other lvm things which > > you need dm for, so why use both when one will do? That's my take on it. > > 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. > > 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. > 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. That's a valid point to make but it can ;) > It can be achieved by giving md/raid5 the right interfaces so that > metadata can be managed from userspace (and I am nearly there). Yeah, and I'm nearly there to have a RAID4 and RAID5 target for dm (which took advantage of the raid address calculation and the bio to stripe cache copy code of md raid5). See http://people.redhat.com/heinzm/sw/dm/dm-raid45/dm-raid45_2.6.15_200601201914.patch.bz2 (no Makefile / no Kconfig changes) for early code reference. > Then 'dmraid' (or a similar tool) can use 'dm' interfaces for some > raid levels and 'md' interfaces for others. Yes, that's possible but there's recommendations to have a native target for dm to do RAID5, so I started to implement it. > > NeilBrown > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Regards, Heinz -- The LVM Guy -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@xxxxxxxxxx +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
