Files-11 ODS Level 1 (VAX Only) Versus Levels
2 and 5
On
VAX systems, for reasons of performance, reliability, and security,
Files--11 ODS Level 2, a compatible superset of ODS Level 1, is
the preferred disk structure on the system. At volume initialization
time, Structure Level 2 is the default. (Refer to the INITIALIZE
command in the HP OpenVMS DCL Dictionary.)
On VAX systems, specify ODS Level 1 only for volumes that
must be transportable to RSX--11M, RSX--11D, RSX--11M--PLUS, and
IAS systems, as these systems support only that structure level.
Additionally, you might be required to handle Structure Level 1
volumes transported to OpenVMS from one of these systems.
Table 4 Limitations on Files--11 Structure Level 1 Volumes
Disk
Only Files--11 ODS--2 disks
are protected objects.
Directories
No hierarchies of directories
and subdirectories, and no ordering of directory entries (that is,
the file names) in any way. RSX--11M, RSX--11D, RSX--11M--PLUS,
and IAS systems do not support subdirectories and alphabetical directory
entries.
Disk quotas
Not supported.
Multivolume
files and volume sets
Not supported.
Placement control
Not supported.
Caches
No caching of file header
blocks, file identification slots, or extent entries.
System disk
Cannot be a Structure Level
1 volume.
OpenVMS Cluster access
Local access only; cannot
be shared across a cluster.
Clustered allocation
Not supported.
Backup home
block
Not supported.
Protection
code E
E means "extend" for
the RSX--11M operating system but is ignored by OpenVMS.
File versions
Limited to 32,767; version
limits are not supported.
Enhanced protection features
(for example, access control lists)
Not supported.
Long file names
Not supported.
RMS journaling
Not supported.
RMS execution statistics
monitoring
Not supported.
Future enhancements to OpenVMS software will be based primarily
on Structure Level 5; therefore, Structure Level 1 volumes might
be further restricted in the future.
HP OpenVMS System Manager's Manual, Volume 2:... 
Files-11 Disk Structure
