When you want to print or copy files located on an unlabeled tape or a tape with nonstandard labels, you must use the FR or UL specification for the input file. To use these tapes successfully with DUMPALL, you must understand the location of the tape marks and data records on the input tapes so that you can position the tape correctly.
The following terms are necessary to your understanding the DUMPALL syntax required to create and read tapes:
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Tape mark
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Unlabeled tape
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Labeled tape
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Nonstandard labeled tape
For a description of multivolume tapes, refer to the I/O Subsystem Programming Guide.
A tape mark is a special physical record that a system or program writes on a magnetic tape volume to delimit logical entities, such as files, from one another. By convention, the last valid data block or label record on a tape is followed by two tape marks in sequence.
An unlabeled tape is a tape that has no label records. An unlabeled tape does not have a serial number.
A single-file unlabeled tape contains one file and has the following format:
data blocks for file tape mark tape mark
A multifile unlabeled tape is a tape that contains more than one file and no label records. A multifile unlabeled tape has the following format:
data blocks for first file
tape mark
data blocks for second file
tape mark
.
.
.
data blocks for last file
tape mark
tape markThe PER MT system command entered at an ODT for an unlabeled tape produces a display similar to the following:
-------------------------- MT STATUS -----------------------
84 P 1600 1 UNLABELED
A labeled tape is a tape that has label records. The label records contain information needed to locate a specific file on the tape. Each file on a labeled tape is preceded and followed by a set of label records. A tape mark is used to separate the label records from the records of a file on the tape. Refer to the I/O Subsystem Programming Guide for information on standard tape label formats.
Note that library maintenance tapes, which are labeled tapes, contain label information that is unique to library maintenance tapes. A library maintenance tape cannot be read as a labeled tape by DUMPALL, and a labeled tape as described in the preceding paragraph cannot be read by the library maintenance utility.
A single-file labeled tape contains one file and label records and has the following format:
VOL label records for tape HDR label records for file tape mark data blocks for file tape mark EOF label records for file tape mark tape mark
A multifile labeled tape contains more than one file and label records. A multifile labeled tape has the following format:
VOL label records for tape
HDR label records for first file
tape mark
data blocks for first file
tape mark
EOF label records for first file
tape mark
HDR label records for second file
tape mark
data blocks for second file
tape mark
EOF label records for second file
tape mark
.
.
.
HDR label records for last file
tape mark
data blocks for last file
tape mark
EOF labels for last file
tape mark
tape markThe PER MT system command entered at an ODT for a labeled tape produces a display similar to the following:
------------------------ MT STATUS -----------------------
84 P [SERNUM] 1600 1 1:0 T/FILEONEWhen it creates a label record for a multifile tape, the operating system uses only the first and last identifiers from the file title for each file written to the tape. For example, the file F/X/Y/Z/A is labeled F/A on the tape. Furthermore, if the first identifier in the title of each file on the tape is the same, a program need only set the internal file title of the program to the first and last identifiers (as it stands on the tape) to access a particular file on the tape. When the system opens a file, the system automatically positions the tape to read the first record of the required file. For example, if a labeled multifile tape contains the files F/A, F/B, F/C, and F/D, a program that opens an internal file with a KIND attribute value of TAPE and a TITLE attribute value of F/C accesses the records contained in file F/C on the tape.
When you create a labeled tape, you can use a single identifier for each file title. In this case, DUMPALL can read files other than the first file on the tape only if you specify the MULTIFILE option and the operator replies with an IL (Ignore Label) system command to the “NO FILE” RSVP message.
Some of the advantages of labeled tapes are the following:
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Labeled tapes have a serial number recorded in the VOL label that helps you and your installation keep track of tape volumes.
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Because the file name is stored in the HDR labels of a file, labeled tapes enable you to reference and locate tape files by name.
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Because the HDR and EOF labels record the values of file attributes such as record size, block size, and creation date, programs such as DUMPALL can automatically determine the proper attributes to be used to access a file stored on labeled tape volumes.
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The system automatically handles switching from one volume to the next whenever a read, write, or copy action reaches the end of a labeled tape volume.
Some tapes created by systems other than ClearPath MCP might have labels that are not fully compatible with the ClearPath MCP system. For such tapes, you can use the PER MT system command to show the tapes as labeled or unlabeled. However, DUMPALL might not be able to retrieve files by name from such tapes, or DUMPALL might not be able to determine the correct record size and block size of the files on such tapes. To copy or print such tapes, you might need to use the UL or FR option to indicate that DUMPALL is to ignore the labels. If you use the UL or FR option, you might also need to use the SKIPTM option to position the tape past the tape mark that separates the label records from the data blocks for the files. Also, you must specify the MAXRECSIZE and BLOCKSIZE file attributes for the files on nonstandard labeled tapes. Refer to “Treating Labeled Tapes as Unlabeled Tapes” later in this section.
