Q:

When do I need to run nodetool upgradesstables while upgrading multimode cluster?

I am in process of upgrading Cassandra from 2.0.9 to 2.1.14.  In the upgrade instructions, it says we should run nodetool upgradesstables after the upgrade process.
I have 12 nodes in my cluster.  When I start the upgrade process on a node, do I need to run nodetool upgradesstables on that node after starting it with the new version?  Or after all nodes have been upgraded to the new version?

A:

You'll want to do it after all nodes have been upgraded.
nodetool upgradesstables can take a while to complete (depending on the size of your data).  But the good news is that Cassandra 2.1 can read 2.0 sstables, so you can run it at your leisure (good idea to do so during off-hours).
That being said, make sure it runs to completion on all nodes, as your next upgrade (2.2) depends on it (2.2 cannot read 2.0 sstables).

