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From Ilya Kasnacheev <ilya.kasnach...@gmail.com>
Subject Re: Distribution of backups
Date Thu, 17 May 2018 16:21:09 GMT
Hello David!

Yes, I think that should be possible to implement. However, when a node
fails there would be a massive backlog of rebalancing on just two nodes,
and it might cause a problem on its own. Random placement guarantees that
rebalancings are placed evenly in case of node failure

Regards,

-- 
Ilya Kasnacheev

2018-05-17 19:11 GMT+03:00 David Harvey <dharvey@jobcase.com>:

> We built a cluster with 8 nodes using Ignite persistence and 1 backup, and
> had two nodes fail at different times, the first being storage did not get
> mounted and ran out of space early, and the second an SSD failed.   There
> are some things that we could have done better, but this event brings up
> the question of how backups are distributed.
>
> There are two approaches that have substantially different behavior on
> double faults, and double faults are more likely at scale.
>
> 1) random placement of backup partitions relative to primary
> 2) backup partitions have similar affinity to the primary partitions,
> where in the extreme nodes are paired so that primaries on the node pair
> have backups on the other node of the pair
>
> With a 64 node cluster, #2 would have 1/63th of the likelihood of data
> loss when 2 nodes fail vs #1.
>
> I'm guessing that ignite ships with #1, but we could provide our own
> affinity function which would accomplish #2 if we chose?
>
>
>
>
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