  On-disk differences between ODS-2 and ODS-5? 
 The Question is:
 
Is there any documentation available on the physical layout of ODS5 disk
volumes?
 
tnx
 
 The Answer is:
 
  The OpenVMS Wizard is not aware of any availablity of this material
  at present (as of July 2001), though discussions are underway with
  outside organizations to provide this information.
 
  There have been a number of changes throughout RMS and elsewhere in
  OpenVMS itself, though the change from ODS2 to ODS5 within the disk
  file structure itself are effectively confined to one data structure
  that is (newly) present on the ODS5 disk -- remember that ODS5 is a
  direct and linear decendent of ODS2, and ODS2 is intended to be a
  proper subset of ODS5.
 
  The salient difference in the on-disk file structure involves the
  structure that holds the longer filenames: ODS2 disks utilize the
  $FI2DEF structure, while ODS5 volumes use both the existing $FI2DEF
  and the new $FI5DEF structures.  Please see the $FI2DEF and $FI5DEF
  structure definitions in the system libraries for details.
 
  Also note that the identification-related constants in the volume's
  home block ($HM2DEF) do differ slightly between ODS2 and ODS5 volumes,
  to permit MOUNT and other tools to differentiate ODS2 from ODS5 volumes.
 
  Please also see the OpenVMS Source Listings CD-ROM kit (for V7.2 and
  later) for details of the OpenVMS changes, and (if you are able to
  locate a copy) Kirby McCoy's VMS File System Internals book for the
  low-level details of the ODS2 file structure.  (ODS2 documentation is
  also available on various versions of the OpenVMS Freeware.)
 
  Also please see topic (2678).
 
