Determine BL and RL of a file Post: 302388864

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Top Forums Shell Programming and Scripting Determine BL and RL of a file Post 302388864 by Linux-wannabe on Thursday 21st of January 2010 04:45:14 PM

01-21-2010

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Determine BL and RL of a file

A regular ebcdic mainframe tape usually contains header information the 1st three blocks of the tape. The header information tells the computer/user more information about what is on tape. The header info is 240 bytes in length at 80 bytes each header. The 1st block/header is volume name or volser (usually matches barcode), the next block contains information about the dataset on tape (eg block is 80 bytes and positions 5-21 contain data set identifier-The last 80 block of header information contains information on how the tape is written (80 bytes - Position 5-record format (fixed-or variable), position 6-10 is equal to block length, and positions 11-15 contain record length. I could usually find out the record length and block length of the tape by doing something like dd if=/dev/st0 bs=240 conv=ascii of=/root/header_info.

Think of blocks of data as managing data across the length of the tape and record length where next record of data to be processed or worked with begins....

Sometimes you can figure this out (more frequently if you have an un-labeled tape) by viewing the data on tape in a viewer and as you step thru the tape you determine the tape is fixed (same block size) and can determine the record length by trial and error=look at what you think 1st record ends and then divide by block size-if this is divisible you probably got the correct number...

Now a segy tape has two blocks of data that identify a tape. The 1st block is 3200 length and is usually ebcdic although it can be ascii, the next block is 400, and then comes the data. You can go to www.seg.org and do a search on segy header and it will point you to a document on how the data is put on tape and positions of information about tape (like above). Cannot save and open this document-wants a password-but if you want to view online-just open the word document from your browser....

Anyway I am trying to figure if there is a way to determine the correct block length and record length of a flat file (already on disk-not tape) with some kind of unix-linux script. Here the data would already be on disk-want to be able to format the data correctly if I put on tape. This would be cool and would help me with processing of data-

Thanks in advance-

Bryan

Last edited by Linux-wannabe; 01-25-2010 at 02:00 PM.. Reason: Bad example

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LEARN ABOUT FREEBSD

tcopy

TCOPY(1)						    BSD General Commands Manual 						  TCOPY(1)

NAME

     tcopy -- copy and/or verify mag tapes

SYNOPSIS

     tcopy [-cvx] [-s maxblk] [src [dest]]

DESCRIPTION

     The tcopy utility is designed to copy magnetic tapes.  The only assumption made about the tape layout is that there are two sequential EOF
     marks at the end.	By default, the tcopy utility will print information about the sizes of records and files found on the /dev/sa0 tape, or
     on the tape specified by the src argument.  If a destination tape is also specified by the dest argument, a copy of the source tape will be
     made.  The blocking on the destination tape will be identical to that used on the source tape.  Copying a tape will yield the same program
     output as if just printing the sizes.

     The following options are available:

     -c 	Copy src to dest and then verify that the two tapes are identical.

     -s maxblk	Specify a maximum block size, maxblk.

     -v 	Given the two tapes src and dest, verify that they are identical.

     -x 	Output all informational messages to the standard error instead of the standard output.  This option is useful when dest is given
		as /dev/stdout.

SEE ALSO

     mt(1), mtio(4)

HISTORY

     The tcopy command appeared in 4.3BSD.

BUGS

     Writing an image of a tape to a file does not preserve much more than the raw data.  Block size(s) and tape EOF marks are lost which would
     otherwise be preserved in a tape-to-tape copy.

     End of data (EOD) is determined by two sequential EOF marks with no data between them.  There used to be old systems which typically wrote
     three EOF's between tape files.  The tcopy utility will erroneously stop copying early in this case.

     When using the copy/verify option -c, tcopy does not rewind the tapes prior to start.  A rewind is performed after writing, prior to the ver-
     ification stage.  If one does not start at the beginning-of-tape (BOT) then the comparison may not be of the intended data.

BSD
								 December 20, 2006							       BSD