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From: gene@zeno.mn.org (Gene H. Olson)
Newsgroups: comp.unix.xenix.sco
Subject: Re: Compressing to a Tape Drive
Message-ID: <1991Mar9.082246.3581@zeno.mn.org>
Date: 9 Mar 91 08:22:46 GMT
References: <183@mnopltd.UUCP> <1991Feb22.223900.12296@mrspoc.Transact.COM>
Organization: Smartware Consulting
Lines: 21

itkin@mrspoc.Transact.COM (Steven M. List) writes:

>tar and cpio used fixed size blocks.  dd by default writes a partial block
>if the last block is not fully sized.  In this case it sometimes helps to
>use the "conv=sync" option to dd.  This forces ALL blocks to be the same
>size and will force the last block out to full size.

Be careful using conv=sync when dd is fed by a pipe.  If for any
reason it reads a partial block from the pipe (and there are lots
of ways that can happen) it will pad out that block to full size.
If that happens in the middle of your archive, you are screwed,
and you may not discover it until you really need that archive.

Ideally, your data compression program should do the padding for
you.  The "compact" program I posted to the net some time ago does
that automatically.
_________________________________________________________________________
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  /  )                Gene H. Olson             gene@zeno.mn.org
 / __  _ __  _                             
(__/ _(/_//_(/_                                 gene@digibd.com