HP OpenVMS Systems Documentation
OpenVMS System Manager's Manual
|Allocating and deallocating disk and tape drives||Section 9.2|
|Initializing volumes||Section 9.3|
|Protecting volumes||Section 9.4|
|Mounting volumes||Section 9.5|
|Setting up disk volume sets||Section 9.6|
|Mounting ISO 9660 volume sets and groups||Section 9.7|
|Mounting tape volume sets||Section 9.8|
|Dismounting volumes and volume sets||Section 9.9|
|Using command procedures for media setup||Section 9.10|
|Managing disk space||Section 9.11|
|Using the Analyze/Disk_Structure utility to check and repair disks||Section 9.12|
|Using mount verification for recovery||Section 9.13|
|Using Interrupt Priority Level C (IPC)||Section 9.14|
|Using the Bad Block Locator utility to detect media errors||Section 9.15|
This chapter explains the following concepts:
|Disks and CD-ROMs||Section 9.1.1|
|Extended File Specifications on OpenVMS Alpha systems||Section 9.1.2|
|Magnetic tape||Section 9.1.3|
|Public and private disk volumes||Section 9.1.4|
|Tape and disk volume protection||Section 9.4|
|Disk volume sets||Section 9.6.1|
|Disk quotas||Section 9.11.1|
|Mount verification||Section 9.13.1|
The following list contains concepts related to storage media in general:
|Device (or Drive)||Hardware that allows access to storage media.|
|Media||Physical items on which you can store data.|
|Volume||Logical unit of data storage; one or more media units. A disk or tape must be mounted on a device for the operating system to recognize itas a volume.|
The following sections use these terms to explain media concepts.
9.1.1 Disk and CD-ROM Concepts
This section defines terms related to disks and
CD-ROMs. It also compares on-disk file structures and
explains the ISO 9660 standard.
18.104.22.168 Disk Terminology
Disks are physical media on which files reside. On--Disk Structure (ODS) refers to a logical structure given to information stored on a disk; it is a hierarchical organization of files, their data, and the directories needed to gain access to them. The OpenVMS file system implements the ODS and provides access control to the files located on the disk.
Compact disc read-only memory (CD-ROM) discs and readers used with computers are very similar to the CD-ROMs used for audio applications. The major differences are that CD-ROM drives have a digital (rather than an audio) interface, and that CD-ROM discs employ additional layers of error correction and formatting to encode data blocks.
The advantages of storing data on CD-ROMs rather than on tape or other removable media are:
Table 9-1 defines terms as they apply to disks and CD-ROMs.
|Sector||Uniquely addressable unit. Each sector on a CD-ROM comprises a sequence of 2048 8-bit bytes; on most disks, a sector is equivalent to a block (512 bytes).|
|Logical block||Organizational unit of volume space containing 512 8-bit bytes. A CD-ROM sector comprises 4 blocks.|
|Logical block numbering||Logical blocks are numbered from 0 to n-1.|
|Cluster 1||Logical grouping of blocks; basic unit by which disk (not CD-ROM) space is allocated.|
|Extent||Contiguous logical blocks allocated to a particular file.|
|File||Array of consecutive virtual blocks 2, numbered 1 to n, plus a set of attributes with values. A file is either a data file or a directory file. Directories can contain both data files and directory files.|
|Volume||Disk that has been prepared for use by placing a new file structure on it.|
|Volume set||Combination of several volumes; has the appearance of one large volume.|
Information on a disk or CD-ROM can be accessed as
logical blocks on the disk or as virtual blocks of files on the disk.
22.214.171.124 Disk and CD-ROM File Structures
On-Disk Structure (ODS) refers to a logical structure given to information stored on a disk or CD-ROM. It is a hierarchical organization of files, their data, and the directories needed to gain access to them. The OpenVMS file system implements the On-Disk Structure and provides access control to the files located on the disk.
Figure 9-1 shows the hierarchy of blocks, clusters, extents, and files in the On-Disk Structure. The number of blocks in any one extent is a multiple of the cluster size. The figure assumes a cluster size of 2 blocks.
Figure 9-1 On-Disk Structure Hierarchy of a File
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.
|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.|
|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 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.
|Reserved File||File Name||+Structure
Levels 2 and 5
|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|
|Backup log file||BACKUP.SYS;1||X|
|Pending bad block||BADLOG.SYS;1||X|
|Volume security profile||SECURITY.SYS;1||X|
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.
Beginning with OpenVMS Version 7.2, the limits of storage and index file bitmaps have been increased as follows:
|Type of Bitmap||Limit|
|Storage bitmap||65535 blocks|
|Index file bitmap||4095 blocks|
The increased bitmap limits have the following advantages:
The behaviors of the INITIALIZE and BACKUP commands reflect the larger bitmap sizes. Refer to the OpenVMS DCL Dictionary for INITIALIZE command details and the OpenVMS System Management Utilities Reference Manual for BACKUP utility details.
The following message is displayed on pre-Version 7.2 systems when you attempt to access a disk that was initialized on a Version 7.2 or later system:
%MOUNT-F-FILESTRUCT, unsupported file structure level
The increased size of the BITMAP field is incompatible with earlier versions of OpenVMS.
Check the size of BITMAP.SYS on the disk you want to access. If the
size is 256 or greater and you want to access the disk from a
pre-Version 7.2 system, you must copy the data to a disk with a
BITMAP.SYS that is less than 256 blocks. If you use the DCL command
BACKUP/IMAGE, be sure to use the /NOINITIALIZE qualifier.
126.96.36.199 Comparison of ODS-1, ODS-2, and ODS-5 Formats
Table 9-4 compares specific characteristics of On-Disk Structure (ODS) Levels 1, 2, and 5.
|Characteristic||ODS-1 (VAX only)||ODS-2||ODS-5|
|File name length||9.3||39.39||238 bytes, including the dot and the file type. For Unicode, 236 bytes is 119 characters, including the dot and the file type.|
|Character set||Uppercase alphanumeric||Uppercase alphanumeric plus hyphen (-), dollar sign ($), and underscore (_)||ISO Latin-1, Unicode (refer to the description in OpenVMS Guide to Extended File Specifications.)|
|File versions||32,767 limit; version limits are not supported||32,767 limit; version limits are supported.||32,767 limit; version limits are supported.|
|Directories||No hierarchies of directories and subdirectories; directory entries are not ordered 1||
VAX: 8 (with rooted logical, 16)
VAX: 8 (with rooted logical, 16)
|System disk||Cannot be an ODS-1 volume||Can be an ODS-2 volume||ODS-5 volume not supported for Version 7.2|
|Page file, swap file, dump file, parameter (.PAR) file, and other system files||Supported||Supported||Not supported|
|OpenVMS Cluster access||Local access only; files cannot be shared across a cluster||Files can be shared across a cluster||Files can be shared across a cluster. However, only computers running OpenVMS Version 7.2 or later can mount ODS-5 disks. VAX computers running Version 7.2 or later can see only files with ODS-2 style names.|
|Disk||Unprotected objects||Protected objects||Protected objects|
|Disk quotas||Not supported||Supported||Supported|
|Multivolume files and volume sets||Not supported||Supported||Supported|
|Placement control||Not supported||Supported||Supported|
|Caches||No caching of file identification slots or extent entries||Caching of file header blocks, file identification slots, and extent entries||Caching of file header blocks, file identification slots, and extent entries|
|Clustered allocation||Not supported||Supported||Supported|
|Backup home block||Not supported||Supported||Supported|
|Protection code E||E means "extend" for the RSX--11M operating system but is ignored by OpenVMS||E means "execute access"||E means "execute access"|
|Enhanced protection features (for example, access control lists)||Not supported||Enhanced protection features supported||Enhanced protection features supported|
Future enhancements to OpenVMS software will be based primarily on Structure Levels 2 and 5; therefore, Structure Level 1 volumes might be further restricted in the future. However, Compaq does not intend for ODS-5 to be the default OpenVMS file structure. The principal function of ODS-5 is to enable an OpenVMS system to be a server for other systems (such as Windows NT) that have extended file names.
The OpenVMS implementation of On-Disk Structure conforms to the file structures defined by the ISO 9660 standard. Table 9-5 defines terms related to the ISO 9660 standard.
|Volume space||Set of all logical blocks on a volume containing information about the volume.|
|System area||One of two divisions of CD-ROM volume space; includes logical sectors 0 through 15; reserved for system use.|
|Data area||One of two divisions of CD-ROM volume space; includes the remaining volume space, beginning with logical sector 16.|
Two aspects of an implementation are required to support ISO 9660 file structures in an OpenVMS environment: partially recorded data blocks and data interleaving.