HADOOP-16107. FilterFS passes through the concat operation, and checksum FS doesn't override that call -so files created through concat do not have checksums.
If people are using a checksummed fs directly with the expectations that they will, that expectation is not being met.
What to do?
- fail always?
- fail if checksums are enabled?
- try and implement the concat operation from raw local up at the checksum level
append() just gives up always; doing the same for concat would be the simplest. Again, brings us back to "need a way to see if an FS supports a feature before invocation", here checksum fs would reject append and concat