NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/os/vms/20316

Text File | 1993-01-04 | 1.7 KB | 39 lines

Newsgroups: comp.os.vms
Path: sparky!uunet!zaphod.mps.ohio-state.edu!rpi!utcsri!newsflash.concordia.ca!sifon!thunder.mcrcim.mcgill.edu!sobeco!szweep
From: [e-mail] (Steve Zweep)
Subject: Variable length records to tape
Organization: Sobeco Ernst & Young
Distribution: na
Date: Mon, 4 Jan 93 22:48:31 GMT
Message-ID: <[e-mail]>
Keywords: VMS VARIABLE LENGTH PHYSICAL RECORDS FOREIGN SYSTEM
Lines: 27

Can someone tell me how to write variable length physical blocks to tape
with VMS, so that the tape can be read again on a foreign system?

In better detail:

If my file has record format "Variable length, maximum 2048 bytes", and I
have a record that is 2100 bytes, then I need the first 2048 bytes written
in one physical block and the next 52 bytes written in the next physical
block, immediately followed by a physical end-of-block.  No leading size-
of-block info, no trailing filler to complete 2048 bytes; just my data and
physical end-of-block markers.  On disk, my file is stored just as I want
it:  logical blocks are headed by 2 bytes to indicate their size, but
these 2 bytes are not included in that size -- just my data.  I need VMS
to write this file to tape using these 2 bytes to determine how long to
make the physical block, with no extraneous overhead.  The size of the
physical block would tell the system reading the tape how long the logical
block is.  VMS will *read* a file this way, but when I use COPY to write
one to tape and use "dd" to read it back on a UNIX system, each logical
block is headed by it's size, and this header takes physical space in the
block.  The last block in a record is padded to fill 2048 bytes.

Thanks,

- Andy Marchewka
--
Andy Marchewka, [e-mail]
multiLIS Group, Sobeco Ernst and Young