Technical data

Managing Storage Media
9.1 Understanding Storage Media Concepts
Figure 9–1 On-Disk Structure Hierarchy of a File
ZK−0739−GE
File
Block BlockBlock BlockBlock BlockBlock Block
Cluster 1A Cluster 1B
Block
Cluster 2A
Cluster 1C
Block
Cluster 3A
Cluster 3B
Block Block
Extent 1 Extent 2 Extent 3
OpenVMS File Structure Options
On-Disk Structures include Levels 1, 2, and 5. (Levels 3 and 4 are internal names
for ISO 9660 and High Sierra CD formats.) ODS-1 and ODS-2 structures have
been available on OpenVMS systems for some time. With OpenVMS Version 7.2
on Alpha systems, you can now specify ODS-5 to format disks as well.
The OpenVMS Alpha operating system recognizes all the file structures for disks
and CD–ROMs shown in Table 9–2 except ODS-1. On VAX systems, you can
mount ODS-5-enabled volumes, but you cannot access ODS-5-specific features.
You can use one or more formats to incorporate a volume and file structure that
is compatible with the input/output processing used by the system.
Table 9–2 File Structure Options on OpenVMS Systems
Structure Disk or CD Description
ODS-1 Both VAX only; use for RSX compatibility: RSX–11M, RSX–
11D, RSX–11M–PLUS, and IAS operating systems.
ODS-2 Both Use to share data between VAX and Alpha with full
compatibility; default disk structure of the OpenVMS
operating system.
ODS-5 Both Superset of ODS-2; use on Alpha systems when
working with systems like NT that need expanded
character sets or deeper directories than ODS-2.
ISO 9660 CD CD ISO format files: use for platform-independent
publishing and distribution; supported by other
systems.
High Sierra CD A variant of ISO 9660.
Dual format CD Single volume with both ISO 9660 CD and ODS
formats. You can use both formats to access files
whose directories might point to the same data.
(continued on next page)
9–4 Managing Storage Media