Galera Replication error: log block numbers mismatch
I finally have solved this problem.

I found an article on launchpad that said to use this command to see if the problem was IO:
innobackupex --user=&lt;username&gt; --password=&lt;password&gt; --stream=tar -- ibbackup=/usr/bin/xtrabackup /tmp &gt;/dev/null

This failed to, so I started thinking IO was not at fault.

I played around with this command and found this one to complete:
innobackupex --user=&lt;username&gt; --password=&lt;password&gt; --stream=xbstream --parallel=15 /tmp &gt;/dev/null

This also showed that my ulimit was not high enough, so I had to set this higher for the backup to complete.

To force innobackupex to use xbstream instead of tar for the --stream option I but this in my.cnf on both of my galera servers:
[sst]
streamfmt=xbstream