Extended (v5) directories have better performance than v4 directories of the same size. For optimal performance after all systems at your site have been migrated to z/OS® V2R1, all of the directories should be converted from v4 to v5 even though support will continue to be provided for v4 directories. To convert selected file systems or directories, you can use automatic methods (such as specifying the MOUNT parameters or by using the offline conversion utility). You can also convert them explicitly with the zfsadm convert command.

If your installation exports zFS file systems to NFS or SMB, it is recommended that the zfsadm convert command not be used for conversions for directories that are exported by these servers. In rare cases, remote applications can get unexpected errors if a directory being manually converted is simultaneously being accessed by NFS or SMB users. Use one of the other methods for the conversion, such as offline conversion or the CONVERTTOV5 MOUNT parameter, for these file systems. These methods will ensure that each individual directory is completely converted before it can be exported.

If you are not planning to convert all file systems to v5, then it is best to at least do the most active file systems or the file systems with large directories. A directory will get a nontrivial benefit by conversion to v5 if it has 10000 entries or more (a length of approximately 800 K or more). You can determine the most active file systems by issuing MODIFY ZFS,QUERY,FILESETS or by using the wjsfsmon tool. The number of entries in a directory can be determined by issuing the command df -t. The approximate rate of conversion for the directories is between 3500 (for a z9® machine) and 10000 (for a zEC12 machine) directory entries per second, depending on your processor.

After you decide that a file system is going to be converted to v5, you need to decide what conversion method to use. If the file system can be unmounted, the ioefsutl converttov5 batch utility or MOUNT parameters can be used. If it cannot be unmounted and it is not exported by NFS or SMB servers, use the zfsadm convert command. If it is exported by NFS or SMB servers, add the converttov5 attribute to the mounted aggregate. See Changing zFS attributes on a mounted zFS compatibility mode file system for instructions about how to add the converttov5 attribute to the mounted file system.