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Backup ideas: using a double-stacked setup

Have you ever wanted to do a file based backup of your data without impacting
your application, and without stopping your HA replication? Here is one
possible method.

For DRBD 8.4.2 we’ve removed the double-stacked check in the userspace tools; now it’s easier to do a multi-stacked setup.

Here is

  • a HA cluster, consisting of nodes A and B;
  • a DR node, attached via DRBD proxy; and
  • a Backup node.

The special thing here is that the dashed DRBD backup connection is not always connected; via a cronjob the backup node disconnects itself, does a (file-based) backup of the data to another storage (tape, harddisk, DVD-RW, paper tape…), and reconnects afterwards – to get the newer data, by a standard synchronization.

The advantage is that the IO load on the backup node has no impact on the primary node – you can even start a local database, and do some CPU- and IO-intensive evaluations. As the backup node is not connected to the HA cluster it cannot slow down the normal operation.

The backup itself can be taken with automatic LVM Snapshots, which prevents a split brain situation when mounting the backup drbd resource – or you need to do a drbdadm connect --discard-my-data before re-connecting.

And: all of that is possible while having a continuous connection to the disaster-recovery site.

Credit for this also goes to Mark Olliver from Thermeon, who was involved in testing and developing this setup.

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