This task is to verify the client should be running okay when mirrored files are being accessed by old version of Lustre. There should be no system crash or any other problems that stops old file system from accessing plain and PFL files. However, it's acceptable for old clients to see IO errors when it is trying to access mirrored files.

Andreas once mentioned that when a mirrored file is being accessed by an old client, the MDS should be able to make a fake PFL layout from one of mirror so that old clients can still read the data.