[sheepdog-users] Understanding number of copies and offline node behaviour
Gerald Richter - ECOS
richter at ecos.de
Fri Sep 6 06:32:26 CEST 2013
I am trying to setup a new sheepdog cluster. I am using version 0.6.0.
I have currently 2 host for the start, but the cluster should grow to 4 and more nodes.
Since I cannot change the number of copies later on (as far as I can tell from studying posts from the list), I tried to format the cluster with 3 copies. This causes “IO has halted as there are too few living nodes”. So I reformat with copies = 2 and everything works fine, but if one node goes down I again get “IO has halted as there are too few living nodes”.
My expectation was that the number of copies specifies how many times the same block will be saved to a different node (or zone). So if I specify 3 copies, it will still work if maximum 2 nodes goes down in my cluster, because there is always a third node to pick up the data.
I case of my two node test, I would have expected to continue to work, because if I have 2 copies and 2 nodes, there needs to be all data on both nodes, so if one of them fails the data is still on the other node.
I would be very happy if somebody can enlighten me how the number of copies and the number of online nodes are related.
Thanks & Regards
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