-Re: Migration needed when updating within an Hadoop release
> - But what about minor updates, e. g. from 1.0.1 to 1.0.4? Has this ever happened for such updates?
You will probably see log messages like 'RPC version mismatch', in this case you have to upgrade the filesystem. If not - all well :)
> - What about HBase minor releases in this context? Have data model changes/ conversions/ migrations ever happened between minor releases?
Yes, but not regularly. Please see my next answer.
> - Is there a similar wiki page describing HBase upgrade?
German Hadoop LinkedIn Group: http://goo.gl/N8pCF