On Thu, Apr 26, 2018 at 7:04 PM, Scottix <scottix@xxxxxxxxx> wrote: > Ok let me try to explain this better, we are doing this back and forth and > its not going anywhere. I'll just be as genuine as I can and explain the > issue. > > What we are testing is a critical failure scenario and actually more of a > real world scenario. Basically just what happens when it is 1AM and the shit > hits the fan, half of your servers are down and 1 of the 3 MDS boxes are > still alive. > There is one very important fact that happens with CephFS and when the > single Active MDS server fails. It is guaranteed 100% all IO is blocked. No > split-brain, no corrupted data, 100% guaranteed ever since we started using > CephFS > > > Now with multi_mds, I understand this changes the logic and I understand how > difficult and how hard this problem is, trust me I would not be able to > tackle this. Basically I need to answer the question; what happens when 1 of > 2 multi_mds fails with no standbys ready to come save them? > What I have tested is not the same of a single active MDS; this absolutely > changes the logic of what happens and how we troubleshoot. The CephFS is > still alive and it does allow operations and does allow resources to go > through. How, why and what is affected are very relevant questions if this > is what the failure looks like since it is not 100% blocking. Okay so now I understand what your real question is: what is the state of CephFS when one or more ranks have failed but no standbys exist to takeover? The answer is that there may be partial availability from the up:active ranks which may hand out capabilities for the subtrees they manage or no availability if that's not possible because it cannot obtain the necessary locks. No metadata is lost. No inconsistency is created between clients. Full availability will be restored when the lost ranks come back online. -- Patrick Donnelly _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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