Technical data

Managing Storage Media
9.1 Understanding Storage Media Concepts
Table 9–2 (Cont.) File Structure Options on OpenVMS Systems
Structure Disk or CD Description
Foreign Both Unknown file structure. When you specify a foreign
structure, you make the contents of a volume known
to the system, but the system makes no assumptions
about its file structure. The application is responsible
for supplying a structure.
When you create a file, you normally specify a file name to OpenVMS Record
Management Services (RMS), which assigns this name to the file on an on-disk
volume. RMS places the file name and file ID associated with the newly created
file in a directory, which contains an entry defining the location for each file.
When you access a file, you supply the file name, which supplies a path to the
file identifier through the directory entry. The file identifier, in turn, points to the
location of the file header, which contains a listing of the extent or extents that
locate the actual data.
Reserved Files on OpenVMS Systems
Reserved files control the structure of a On-Disk Structure (ODS) Levels 2 and
5 volumes. (Only five of these files are used for a Level 1 volume.) Table 9–3
identifies all reserved files, and indicates to which ODS level they pertain.
The files listed in Table 9–3 are in the master file directory (MFD), [000000].
Appendix A contains a description of each reserved file.
Table 9–3 Reserved Files
Reserved File File Name
†Structure
Level 1
Structure
Levels 2 and 5
Index file INDEXF.SYS;1 X X
Storage bit map file BITMAP.SYS;1 X X
Bad block file BADBLK.SYS;1 X X
Master file directory 000000.DIR;1 X X
Core image file CORIMG.SYS;1 X X
Volume set list file VOLSET.SYS;1 X
Continuation file CONTIN.SYS;1 X
Backup log file BACKUP.SYS;1 X
Pending bad block BADLOG.SYS;1 X
Volume security profile SECURITY.SYS;1 X
†VAX specific
Limits of Storage and Index File Bitmaps
In previous versions of OpenVMS, both storage and index file bitmaps were
limited to 255 blocks. This size, in turn, limited a volume to approximately one
million allocation units, or clusters. Larger disks were required to have a larger
cluster factor to accommodate the limit; for example, a 9 GB disk required a
cluster factor of 18.
Managing Storage Media 9–5