in place upgrade to CDH4

[alex bohr <al...@gmail.com>]

Hi,
I'm working on upgrading my cluster from CDH3u5 to CDH4.  Trying to do the
upgrade in place rather than creating a new cluster and migrating over.

Doing this on a test cluster right now, but ran into an issue -
First I uninstalled the CDH3 packages and installed the CDH4 ones, then
upgraded the namenode and then started the namenode service.
Then I started the datanode service on one of the data nodes and the
machine started filling up quickly.
It seems like it's re-writing the data into a new format.   Is this
correct, does the upgrade process rewrite the old data into a new format?
 And if so, that means I need a lot of free space on the data nodes that
are being upgrade?

Thanks