Thank you very much for investigating this issue! I was able to solve the issue a few days ago, and I apologize for not updating my status earlier.
To me, the root cause of the issue seems to be the version inconsistency between DAOS server and DASO client header files (daos.h, daos_fs.h, daos_pool.h) that I have used to compile the fio dfs engine. The DAOS server was v.1.2, but the client header files were not. It seems that the fio was trying to connect daos pools with a different version of APIs and failed to connect. After replacing the client headers files with those v.1.2 and recompiling the fio dfs engine, I was able to run the fio dfs engine successfully. Again, thank you very much for your help, and my sincere apologies for not letting you know my status earlier.
Thank you very much,