The following steps helped me to backup AIX 5.3 and AIX 6.1 servers.
1st of all, we need to remove the system limits to allow us to create a large file, our backup.
Edit the limits file:
Allow root user to create unlimited file size by adding “fsize = -1” in its own section:
root: fsize = -1
We can now run our backup using smitty:
Fill in the path in the first field and change next options if needed. Press Enter to start the backup.