Currently while doing HA upgrade, we do not create a new committedTxnId file in the new current directory of JournalNode. And before we have the fix in
HDFS-7042, since the file channel is never closed, for any new journal we're actually updating the committedTxnId file in the previous directory. This can cause NN to fail to start while rollback. HDFS-7042 fixes the main part of the issue: the file channel inside of the committedTxnId object gets closed thus later a new file can be created in the current directory. But maybe it is still better to copy the content file during the upgrade so that we can always use it for sanity check.