Hi Nigel, On 22/06/2015 02:52, Nigel Williams wrote:> I recall a post to the mailing list in the last week(s) where someone said that for an EC Pool the failure-domain defaults to having k+m hosts in some versions of Ceph? > > Can anyone recall the post? have I got the requirement correct?
Yes. The default is equivalent to "no two chunks in the same host". When you have K+M chunks, it means you need at least K+M hosts. It is however better to have K+M+1 hosts or more because CRUSH may fail to map otherwise. You can test the mapping as demonstrated at https://github.com/ceph/ceph/blob/master/src/test/cli/crushtool/bad-mappings.t: if it succeeds with this tool, it will also succeed on your actual cluster. Cheers -- Loïc Dachary, Artisan Logiciel Libre
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