Incompatible changes in
- dfs.block.size should be a multiple of io.byte.per.checksum. Otherwise new files can not be written. No changes to default config.
- DFS layout version changed from -6 to -7. As with any layout change, existing cluster need to be finalized before upgrading the software and cluster should be started with upgrade option after software upgrade.
- Datanode RPC protocol version changed from 7 to 8 (this may not be considered incompatible).
I will add a link to uprade guide for this upgrade.