On Thu, Feb 12, 2009 at 2:45 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Thu, February 12, 2009 8:53 pm, Keld Jørn Simonsen wrote: >> On Thu, Feb 12, 2009 at 08:21:12PM +1100, NeilBrown wrote: >>> On Thu, February 12, 2009 7:11 pm, Keld Jørn Simonsen wrote: >>> > On Thu, Feb 12, 2009 at 02:10:10PM +1100, NeilBrown wrote: >>> >> Comments and testing very welcome. >>> > >>> > 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. >>> >>> That is a fairly simplistic view. >> >> It was also formulated to provoke some thoughts. >> >>> raid1 supports --write-mostly and --write-behind which raid10 is >>> unlikely >>> ever to support. >> >> why? >> >> Anyway would it not be possible that this functionality be implemented >> for raid10,n2? > > It would be possible, but it might not be sensible. > > write-mostly and write-behind only really make sense when you have the > clear distinction between drives that raid1 gives you. > These options don't make sense for raid10 in general. Only in very specific > layouts. > If you like, raid1 is an implementation of a specific raid10 layout, > where it makes sense to add some extra functionality. > >> >> Some code to grow raid10 would also be desirable. Maybe it is some of >> the same operations that need to be applied: getting the old data in, >> have it restructured for the new format, in a safe way, and possibly >> with the help of an extra disk, or possibly not. It sounds non-trivial >> to me too. > > What particular growth scenarios are you interested it? > Just adding a drive and restriping onto that? i.e keep that > same nominal layout but increase 'raid-disks'? > > That would be quite similar to the raid5 grow operation so it shouldn't > be too hard to achieve. > A 'grow' which changed the layout (e.g. near to far) would be a lot > harder. I'd previously seen the wikipedia article regarding Linux RAID10 and its mention of the 3 disk case. Out of academic curiousity, how does the 2 disk RAID10 work? Is it just a matter of have 2 identical volumes and reading subsequent stripes from the alteranate drives? Or is the algorithm more complicated? Wil -- 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
