Re: [PATCH 00/18] Assorted md patches headed for 2.6.30

["Keld Jørn Simonsen" <keld@dkuug.dk>]

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?

> Certainly in many cases raid10 is just as good or better than raid1
> though.
> 
> Certainly a raid10->raid5 conversion for a 2-drive n2 configuration
> is trivial to arrange.  Other conversions are less likely to be supported
> as they require significant non-trivial rearrangement of data.

Yes, possibly.


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.

Best regards
keld
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