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I have upgraded a node in a two-node DRBD cluster as follows:

  1. reinstall Debian
  2. apt-get install drbd-utils
  3. systemctl start drbd
  4. obtain /etc/drbd.d/my_resource.res from backup
  5. configure block device (disk) and IP address for DRBD resource
  6. systemctl reload drbd

At this point DRBD starts to resync and the cluster becomes operational again.

My question is this: what determines if the node acts as DRBD primary or secondary at this point. In my case the opposite node was the primary, so it was important that the upgraded node started as secondary. Is this the default?

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The point which determines which one is the master (primary) one, is which node has started first. IF you start one node, you wait some time and then the other, the first one will be the primary, otherwise it will act as secondary, there is no default behaviour as the DRBD is aware of which node has been the first one to be "online".

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  • So that would mean that DRBD remains up on the primary node while I upgrade the other node, DRBD will always join as secondary on the upgraded node (for the primary is still up). Correct? – rookie099 Jan 14 '19 at 13:33
  • If the master is still up, the second node will always join as secondary right. – Dasel Jan 14 '19 at 13:35

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